Dynamics 101 Vocabulary of Dynamics Processors

Introduction: Rick Naqvi is one of the best people I know to teach on the care and feeding of compressors and limiters, which makes sense, as he works for Presonus, which makes excellent compressors and limiters. He has given us permission to include it here on the ChurchSoundGuy blog. So as to avoid being overwhelming, it will be posted in several installments. This is part 3.

In scientific research, it is widely accepted that if one needs to master a subject quickly, learn the associated vocabulary and industry terms…

1. Compressors

Threshold

The Compressor threshold sets the level at which compression begins. When the signal is above the threshold setting, it becomes ‘eligible’ for compression. Basically, as you turn the threshold knob counterclockwise, more of the input signal becomes compressed. (If you have a ratio setting of greater than 1:1.)

Ratio

Ratio sets the compression slope. This is defined as the output level versus the input level. For example, if you have the ratio set to 2:1, any signal levels above the threshold setting will be compressed at a compression ratio of 2:1. This simply means that for every 1dB of level increase into the compressor, the output will only increase 1/2dB, thus producing a compression gain reduction of 0.5dB/dB. As you increase the ratio, the compressor gradually becomes a limiter. A limiter is defined as a processor that limits the level of a signal to the setting of the threshold. For example, if you have the threshold knob set at 0dB, and the ratio turned fully clockwise, the compressor becomes a limiter at 0dB. This means that the signal will be limited to an output of 0dB regardless of the level of the input signal.

Attack

Attack sets the speed at which the compressor ‘acts’ on the input signal. A slow attack time (fully clockwise) allows the beginning envelope of a signal (commonly referred to as the initial transient) to pass through the compressor uncompressed, whereas a fast attack time (fully counter-clockwise) immediately subjects the signal to the ratio and threshold settings of the compressor.

Release

Release sets the length of time the compressor takes to return the gain reduction back to zero (no gain reduction) after crossing below the compression threshold. Very short release times can produce a very choppy or ‘jittery’ sound, especially in low frequency instruments such as a bass guitar. Very long release times can result in an over compressed sound, sometimes referred to as ‘squashing’ the sound. All ranges of release can be useful at different times however and you should experiment to become familiar with the different sound possibilities.

Hard/Soft Knee

With hard knee compression, the gain reduction applied to the signal occurs as soon as the signal exceeds the level set by the threshold. With soft knee compression, the onset of gain reduction occurs gradually after the signal has exceeded the threshold, producing a more musical response (to some folks).

Auto

Places a compressor in automatic attack and release mode. The attack and release knobs become inoperative and a pre-programmed attack and release curve is used.

Gain

When compressing a signal, gain reduction usually results in an overall reduction of level. The gain control allows you to restore the loss in level due to compression. (Like readjusting the volume.)

Link

When the Link button is pushed in, this channel becomes the slave of the channel to it’s left. All of this channels controls become disabled and metering should be referred to the channel to the left. Essentially, the left channel is the master and the channel with link pushed in is the slave channel in a stereo linked pair.

Compressor Sidechain

The sidechain jack interrupts the signal that the compressor is using to determine the amount of gain reduction to apply. When no connector is inserted into this jack, the input signal goes directly to the compressor’s control circuitry. When a connector is inserted into this jack, the signal path is broken. This signal can then be processed by an equalizer for example to reduce sibilance (de-essing) in a vocal track. The signal is then returned to the unit via the connector. The signal returned to the sidechain could be that of a narrator or vocalist. In this application, the audio that is passing through the compressor will automatically ‘duck’ when the narrator speaks or vocalist sings.

2. Expanders

Downward Expansion

Downward expansion is the most common expansion used in pro audio and recording. This type of expansion applies noise reduction to all signals below a set threshold level.

Ratio

The expansion ratio sets the amount of noise reduction applied to a signal once the signal has dropped below the expansion threshold. For example, a 2:1 expansion ratio attenuates a signal 2dB for every 1dB it drops below the threshold. Ratio’s 4:1 and higher act much like a noise gate without the ability to tailor the attack, hold and release times.

3. Noise Gates

Threshold

The gate threshold sets the level at which the gate opens. Essentially, all signals above the threshold setting are passed through unaffected, whereas signals below the threshold setting are reduced in level by the amount set by the range control. If the threshold is set fully counter-clockwise, the gate is turned off (always open), allowing all signals to pass through unaffected.

Attack

The gate attack time sets the rate at which the gate opens. A fast attack rate is crucial for percussive instruments, whereas signals such as vocals and bass guitar require a slower attack. Too fast of an attack can, on these slow rising signals, cause an artifact in the signal producing an audible ‘click’. All gates have the ability to ‘click’ when opening, however a properly set gate will never click. Below is an example of a gate opening very fast on a pure sine wave. Notice the almost vertical edge of the waveform when the gate opens. This is what produces the high frequency artifact known as ‘click’.

Figure 2.1 shows a gated sine wave. Notice that when the gate opens, an artifact occurs in the waveform sometimes referred to as the gate ‘click’. To avoid the click, add some attack time such that the gate opens at approximately the same frequency as the signal.

Hold

Hold time is used to keep the gate open for a fixed period of time following the signal going below the gate threshold. This can be really useful for effects such as ‘gated snare’ where the gate remains open after the snare hit for the duration of the hold time then abruptly closes.

Release

The gate release time determines the rate at which the gate closes. Release times should typically be set so that the natural decay of the instrument or vocal being gated is not affected. Shorter release times help to clean up the noise in a signal but my cause ‘chattering’ in percussive instruments. Longer release times usually eliminate ‘chattering’ and should be set by listening carefully for the most natural release of the signal.

Range

The gate range is the amount of gain reduction that the gate closes down to. Therefore, if the range is set at 0dB, there will be no change in the signal as it crosses the threshold. If the range is set to -60dB, the signal will be gated (reduced) by 60dB, etc.

Spectral or Frequency Selective Gating

There are many situations, especially with drums, when other instruments open up the gate instead of the instrument being gated. For example, tom-tom mics are generally placed very close to the cymbals on a drum kit, creating the possibility of the cymbals opening up the tom-tom gates. A frequency selective gate will allow the user to specify which frequencies are ‘eligible’ for gating. Therefore the cymbals may be removed from ‘eligibility’ by using a low pass filter to filter out the high frequencies of the cymbals. The gate will no longer open up during cymbal crashes, leaving the low frequencies of the tom-tom to properly open the gates.

Gate Keying

It is sometimes impossible to set a noise gate to open precisely when an instrument sounds in a noisy environment. Most gates feature an external gate key that will allow the gate to be opened using an external signal, in effect ‘triggering’ the gate to open. For example a bass guitar gate might be ‘triggered’ using the kick drum to tighten up the low end of a mix. Or a snare track might be ‘triggered’ using a click track or sequencer to place the snare right in time with the music.

Courtesy Presonus. Used by permission.

____________________________________
David McLain | Technical Geek| CCI SOLUTIONS
Be seen. Be heard.

PO Box 481
/ 1247 85th Ave SE
Olympia, WA 98507-0481

Voice: 800/426-8664 x255 / Fax: 800/399-8273
email: dmclain@ccisolutions.com
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6 Ways to Avoid Wireless Mic Problems

Here are some basic check points from our equipment experts to help you achieve the best wireless performance. Some of the items on this list are no-brainers. Nevertheless, a reminder once in a while doesn't hurt.

We thought this was such an important topic that we included a 7th way to improve your wireless as an added bonus!

Pick the right wireless mic for each application
One type of wireless mic does not fit all. Make sure you match voice types with microphone's that complement them. You also want to make sure that you choose wireless mics with the proper pick-up pattern. That is, unless you don't mind picking up everything else on your stage including the singer who is holding the mic but doesn't sing quite loud enough in the first place. Having a mic with the correct pick-up pattern will help eliminate excess noise (for more on this topic check out The Basic Basics of Microphone Basics). It is also important to decide who can benefit from using headset-style wireless mics. You might also consider using wireless in-ear monitor systems for singer`s and musicians who need the most mobility.

Check all your frequencies for compatibility
You will need to make sure any systems you add to your existing ones are set on different, yet compatible frequencies. [This is especially critical with the changes the FCC has been making to the UHF frequencies.] Wireless systems that are on the same or incompatible frequencies can cause all kinds of awful noise or not work at all. Most modern wireless systems are in the UHF frequency band and can pick up local TV or other commercial stations. We can help you find frequencies that work with your existing system and that don't overlap with stations in your area.

Make sure volumes are set perfectly
Be sure to set the transmitter input levels and/or receiver output levels for the person using the mic and to match the input of your mixer. Loud singers can overload the level into your mixer. Levels that are too low can cause you to use too much input gain and can increase noise. Don't assume that the settings from the factory are correct for your application. Call our experts at 1-800-426-8664. [Note: This connects you to CCI Solutions, the author of this article.]

Load up on fresh batteries
There is nothing worse than dead or weak batteries to interrupt the flow of a worship service or program. Make sure you have plenty of fresh alkaline batteries on hand - the right types for your various wireless systems. If you use rechargeable batteries, be sure primaries and back-ups are fully charged.

EQ your mics carefully
Equalization (EQ) is a useful tool if used judiciously. By choosing good mics with the right characteristics for the application you will be able to faithfully reproduce the voice with little need for tonal adjustment. Properly adjusting the EQ can help reduce some problems and enhance some voices. For instance you can turn down the lows a bit to reduce rumbly handling noise, breath pops & wind noise. Add some highs to brighten mics that are hidden in the hair or under clothes. Sometimes a mid-range adjustment can make speech a little more intelligible. Making small EQ adjustments can make a big difference in the way things sound.

Teach the proper use of wireless microphones
Many problems with wireless mics can come from "user error". One of the most common problems people have is not knowing how to properly turn on and off the mics they are using. Those who aren't used to using wireless may not know that they need to turn the wireless on and off, or where the switch is. Even regular wireless users can forget to turn on the mic before they start singing or speaking.

Handheld mic transmitters and bodypacks usually have two switches - a power switch and a standby switch. Sometimes turning off the power switch when the receiver is on can cause a noise burst in the sound system. The standby switch allows the mic to be muted without actually turning the wireless link off. Many newer wireless systems have electronics that prevent these kinds of problems. Just be sure your team members know which switches to use and where they are on the mic or bodypack. Everyone needs to be taught how to properly hold and speak or sing into the mic, as well as how to handle mics around live monitors or main speakers.

Inspect all your wireless components early
Don't wait 'til just a few days before the big event to get all your wireless stuff out to see if it works. Check all your lapel and headset mic cables two or three weeks before Easter so you're not surprised by a bad mic on the big day.

Make sure you have all the antennae you need for your systems (consider using an antenna combiner with multiple systems). Make sure you have stand clips or holders to set handheld mics in when not in use. You'll need working tie-clips for lapels and possibly wind screens for outdoor services.


from CCI Solutions; used by permission


______________________________________
David McLain Technical Geek CCI SOLUTIONS
Be seen. Be heard.
PO Box 481 / 1247 85th Ave SE
Olympia, WA 98507-0481
Voice: 800/426-8664 x255 / Fax: 800/399-8273
email:
dmclain@ccisolutions.com
online: www.ccisolutions.com
blog:
www.churchsoundguy.com
facebook:
dmclain@ccisolutions.com
linkedin:
http://www.linkedin.com/in/davidmclain
podcast:
http://www.ccisolutions.com/podcast
Clearance Bin:
http://www.ccisolutions.com/clearance

Dynamics 101 Types of Dynamics Processing

Introduction: Rick Naqvi is one of the best people I know to teach on the care and feeding of compressors and limiters, which makes sense, as he works for Presonus, which makes excellent compressors and limiters. He has given us permission to include it here on the ChurchSoundGuy blog. So as to avoid being overwhelming, it will be posted in several installments. This is part 2.

Types of Dynamics Processing

Dynamics processing is the process of altering the dynamic range or levels of a signal thereby enhancing the ability of a live sound system or recording device to handle the signal without distortion or noise, and aiding in placing the signal in the overall mix.

Compression / Limiting

Punch, apparent loudness, presence… just three of many terms used to describe the effects of compression/ limiting.

Compression and limiting are forms of dynamic range (volume) control. Audio signals have very wide peak to average signal level ratios (sometimes referred to as dynamic range which is the difference between the loudest level and the softest level). The peak signal can cause overload in the audio recording or reproduction chain resulting in signal distortion. A compressor/limiter is a type of amplifier in which gain is dependent on the signal level passing through it. You can set the maximum level a compressor/limiter allows to pass through, thereby causing automatic gain reduction above some predetermined signal level or threshold.

Compression refers, basically, to the ability to reduce the output level of an audio signal by a fixed ratio relative to the input. It is useful for lowering the dynamic range of an instrument or vocal, making it easier to record without distorting the recorder. It also assists in the mixing process by reducing the amount of level changes needed for a particular instrument. Take, for example, a vocalist who moves around in front of the microphone while performing, thus making the output level vary up and down unnaturally. A compressor can be applied to the signal to help correct this recording problem by reducing the ‘louder’ passages enough to be compatible with the overall performance.

How severely the compressor reduces the signal is determined by the compression ratio and compression threshold. A ratio of 2:1 or less is considered mild compression, reducing the output by two for signals greater than the compression threshold. Ratios above 10:1 are considered hard limiting. Limiting refers to the point at which the signal is restrained from going any louder at the output.

The level of input signal at which the output is reduced is determined by the compression threshold. As the compression threshold is lowered, more and more of the input signal is compressed (assuming a nominal input signal level). Care must be taken not to ‘over compress’ a signal. Too much compression destroys the acoustical dynamic response of a performance. (‘Over compression’, however, is used by some engineers as an effect, and with killer results!)

Compressor / Limiters are commonly used for many audio applications. A kick drum can get lost in a wall of electric guitars. No matter how much level is increased, the kick drum stays ‘lost in the mud’. Add a touch of compression and tighten up that kick drum sound allowing it to ‘punch’ through without having to crank the level way up.

A vocal performance usually has a wide dynamic range. Transients (the very loudest portion of the signal) can be far outside the average level of the vocal signal. It is extremely difficult to ride the level with a console fader. A compressor/limiter automatically controls gain without altering the subtleties of the performance.

A solo guitar can seem to be masked by the rhythm guitars. Compression can make your ‘lead’ soar above the track without shoving the fader through the roof .

Bass guitar can be difficult to record. A consistent level with good attack can be achieved with proper compression. Your bass doesn’t have to be washed out in the low end of the mix. Let the compressor/limiter give your bass the punch it needs to drive the bottom of the mix.

2. Expansion

There are two basic types of expansion: dynamic and downward. Expansion increases the dynamic range or level of a signal after the signal crosses the expansion threshold.

Dynamic expansion is basically the opposite of compression. In fact, broadcasters use dynamic expansion to ‘undue’ compression before transmitting the audio signal. This is commonly referred to as ‘companding’ or COMPression followed by expANDING.

By far the most common use of expansion is downward expansion. In contrast to compression, which decreases the level of a signal after rising above the compression threshold, expansion decreases the level of a signal after the signal goes below the expansion threshold. The amount of level reduction is determined by the expansion ratio. For example, a 2:1 expansion ratio reduces the level of a signal by a factor of two. (e.g. if a level drops 5dB below the expansion threshold, the expander will reduce it to 10dB below the threshold.) Commonly used as noise reduction, expansion is very effective as a simple noise gate.

The major difference between expansion and noise gating is the fact that expansion is dependent on the signal level after crossing the threshold, whereas a noise gate works independent of a signal’s level after crossing the threshold.

3. Noise Gating

Noise gating is the process of removing unwanted sounds from a signal by attenuating all signals below a set threshold. As described above, the ‘gate’ works independent of the audio signal after being ‘triggered’ by the signal crossing the gate threshold. The gate will remain open as long as the signal is above the threshold. How fast the gate opens to let the ‘good’ signal through is determined by the attack time. How long the gate stays open after the signal has gone below the threshold is determined by the hold time. How fast the gate closes is determined by the release. How much the gate attenuates the unwanted signal while closed is determined by the range.

Courtesy Presonus. Used by permission.

Wireless Update: Final FCC Ruling Includes Protection For Wireless Microphones

Shure: The FCC has established multiple interference avoidance measures designed to protect the broadest possible range of wireless mic users. At the same time, there’s no question that using wireless mics will become more complicated as new types of devices begin sharing the television band. Also includes some operating tips to help maintain performance.

In November, the Federal Communications Commission released the full text of its Second Report and Order approving the use of the “white spaces” – the TV channels that are not actually occupied by a broadcast station – by unlicensed consumer wireless devices.

The FCC now refers to these as “TV Band Devices” or “TVBD’s”. The 130-page document provides details of the technical, operational, and regulatory requirements that the new devices will be subject to.

The FCC’s attention to the needs of wireless microphone users is clearly evident throughout the ruling; in fact, the term “wireless microphone” is used 162 times – more than once per page.

The FCC recognizes that some wireless microphone use is pre-planned and occurs at scheduled events (think concerts, plays, sports events, or business meetings), while some is “itinerant”, meaning that it occurs at random times and places (think TV news crews covering a breaking story).

Accordingly, they have established multiple interference avoidance measures designed to protect the broadest possible range of wireless mic users.

The Order defines two different types of TV Band Devices, which will have slightly different operating characteristics.

Personal/Portable TV Band Devices could include next-generation mobile phones and mobile broadband cards for laptop computers – in other words, devices that move around. These will be limited to 100 milliwatts of transmit power on most TV channels, but will be further restricted to just 40 milliwatts when operating on a TV channel that is adjacent to one occupied by a TV station.

Fixed TV Band Devices could include equipment installed at a home or business (with an outdoor antenna at least 10 meters above the ground) that could transmit or receive wireless broadband internet service or other data.

Fixed TVBD’s will be permitted to operate on TV channels 2, 5-13, 14-36, and 38-51, while Portable units will be limited to channels 21-36 and 38-51 only. (Channel 37 is reserved for radio telescopes and medical telemetry systems; TV stations, wireless microphones, and other devices aren’t allowed.)

Because Fixed TVBD’s will be allowed to transmit at up to four watts of power, they will not be allowed to operate on the ‘adjacent’ channels at all.

TV Band Devices are allowed to go on sale after the DTV transition on February 18, 2009 [now June 12, 2009 -your fearless editor]. Considering the mandatory certification testing required for each new product (which the FCC hopes will take less than 6 months), it will probably be early 2010 before any products reach the market.

The Order makes it very clear that TV Band Devices are not allowed to operate on TV channels that are being used by other ‘authorized users’ at or near the same location.

These include TV stations, Public Safety and municipal agencies (who are allowed to operate two-way radio systems on selected TV channels in 13 U.S. metropolitan areas), and ‘low power auxiliary stations’ (which includes wireless microphones, in-ear monitors, and production intercom systems that operate in the TV band).

To prevent interference, the FCC has devised a clever triple-layer protection scheme that serves both small and large users, who may use wireless mics at scheduled events or operate randomly. People who only need a moderate number of wireless mics or who use them at random times can operate on the channels that will be ‘off-limits’ to TV Band Devices.

Since the Portable TVBD’s aren’t allowed below channel 21, and the Fixed TVBD’s aren’t allowed to use the channels on either side of one occupied by a TV station, there will be (in many cities) a few TV channels between channel 14 and channel 20 that are entirely clear.

In the 13 metro areas where a few of those channels are designated for Public Safety use, the FCC is reserving two additional TV channels for wireless microphone use. These will be the first available channels on each side of channel 37.

So in Chicago, for example, TV channels 16, 18, 20, 35, and 39 will be clear, which would accommodate up to 30 professional-grade wireless mics.

But what about large touring shows that need dozens of wireless mics, in-ear monitors, and intercoms? And what about special events like the Super Bowl, where hundreds of wireless audio, video, and control devices are in use?

To accommodate this kind of use, the FCC will require all TVBD’s to determine their location within 50 meters (using GPS or some other method) and then consult an online database.

The database will send the TVBD a list of available TV channels that are safe to use at that particular location; the device can’t transmit until it receives this list.

A wireless mic user just needs to register the date, time, and location (in latitude and longitude) of their event along with the TV channels being used by their wireless gear in the database, and any TVBD within one kilometer will stay off of those channels.

The Order is quite liberal in defining who will be able to register in the database, referring to “sites with significant wireless microphone use at well defined times and locations.” This is further defined as “instances where one or more microphones are in operation for a period of time not less than one hour.”

For outdoor events that cover a large area such as a race track or golf course, multiple sets of coordinates can be registered in the database to create a larger protected zone.

The database will be created and maintained by a third party, after proposals are solicited and reviewed by the FCC. There could even be multiple providers, but the FCC will require them to synchronize their data every day.

The database administrator can charge TVBD’s a fee to access the database – after all, someone has got to pay for this, right? – but the Order does not mention any fee for a wireless mic user to register.

The Order also requires a “remote kill switch” that can be used against devices that are determined by the FCC to be causing interference. The database administrator would be instructed to send a message of “no channels available” to a single device or to all devices of a particular make and model.

As a third layer of interference prevention, all TVBD’s must utilize spectrum sensing to detect and avoid wireless microphones, TV stations, and other authorized users nearby, whether or not they are registered in the database.

A TV Band Device must scan the spectrum for at least 30 seconds every time it is powered on, and then re-check the channel it is operating on every 60 seconds to make sure that no new microphones have been turned on. If a new mic is detected, the TVBD must cease transmitting on that TV channel within two seconds.

A couple of important issues were not covered in the ‘White Spaces’ Order. The question of when wireless microphones must cease operating in the 700 MHz Band (actually covering 698-806 MHz, or TV channels 52-69) was not addressed.

In August, the FCC proposed that this should occur as of the DTV transition date on February 18, 2009. Given that some wireless microphone users will need to replace significant amounts of equipment in order to comply, many consider this to be an unreasonable – if not impossible – timeline.

The next logical date for the FCC to announce a final decision on this issue would have been at their December 18th meeting, but the 700 MHz matter was not on the meeting agenda.

Nevertheless, wireless mic manufacturers have rapidly created programs to help wireless mic users to comply with the transition, which will occur sooner or later.

The White Spaces Order also does not deal with what some users consider to be the most worrisome issue still hanging: licensing. As most readers are probably aware, the FCC Part 74 Rules created in the 1970’s required wireless microphone users to have a license, and limited eligibility to broadcast stations, TV and film production companies, and cable TV networks.

Decades of problem-free operation with no record of complaints may have allowed the FCC to miss the rapidly expanding use of wireless audio equipment, as well as the fact that most users did not attempt to navigate the incredibly complex 26-page licensing form.

The fact that the FCC intends to allow very liberal access to the database of registered users – with no stated requirement for a license – would seem to indicate that the licensing topic will continue to lay dormant. A final decision in the 700 MHz issue could give the FCC an opportunity to address the licensing issue, but there have not been any announcements of this so far.

There’s no question that using wireless mics will become more complicated as new types of devices begin sharing the television band. Here are some operating tips that will help live sound engineers to maintain stellar performance:

Know the terrain. Before working at any venue, find out what RF transmitters are operating in the TV band nearby. his includes TV stations, Public Safety radios, and Fixed TV Band Devices.

Most major manufacturers offer an online Frequency Finder as well as free software that can help to identify these users. A high-quality scanner that interfaces with a laptop can also help to analyze the real conditions inside a venue, whose steel and concrete may reduce the strength of signals coming from outside.

Get registered. Once the new database is up and running, use it. TV Band Devices need to download the database every day, but that means the need to select TV channels (although not the exact frequencies) at least two days before the show.

Take inventory. Make sure that the wireless gear to be used covers the TV channels that you need to be in. Virtually all professional wireless mics are now frequency agile, but having the widest possible tuning range gives the most flexibility to take advantage of clear channels.

If renting gear, make sure that the provider knows that it may not be okay to substitute the same product in a different frequency range.

The good news is that wireless microphone users have become an important blip on the FCC’s radar. The cultural and financial importance of live entertainment content helped to emphasize the importance of protecting wireless audio systems from interference.

Working together, wireless manufacturers and live sound engineers have ensured the ability for wireless microphones to continue as the reliable, great-sounding tools for live sound.

by Christopher Lyons
From Live Sound International

Dynamics 101: Compressors and Limiters. Introduction.

Introduction: Rick Naqvi is one of the best people I know to teach on the care and feeding of compressors and limiters, which makes sense, as he works for Presonus, which makes excellent compressors and limiters. He has given us permission to include it here on the ChurchSoundGuy blog. So as to avoid being overwhelming, it will be posted in several installments.

Common Questions Regarding Dynamics Processing…

What is dynamic range?

Dynamic range can be defined as the distance between the loudest possible level to the lowest possible level. For example, if a processor states that the maximum input level before distortion is +24dBu and the output noise floor is -92dBu, then the processor has a total dynamic range of 24 + 92 = 116dB.

The average dynamic range of an orchestral performance can range from - 50dBu to +10dBu on average. This equates to a 60dB dynamic range. 60dB may not appear to be a large dynamic range but do the math and you’ll discover that +10dBu is 1000 times louder than -50dBu!

Rock music on the other hand has a much smaller dynamic range, typically - 10dBu to +10dBu, or 20dB. This makes mixing the various signals of a rock performance together a much more tedious task.

Why do we need compression?

Consider the previous discussion: You are mixing a rock performance with a average dynamic range of 20dB. You wish to add an un-compressed vocal to the mix.

The average dynamic range of an un-compressed vocal is around 40dB. In other words a vocal performance can go from -30dBu to +10dBu. The passages that are +10dBu and higher will be heard over the mix, no problem. However, the passages that are at - 30dBu and below will never be heard over the roar of the rest of the mix. A compressor can be used in this situation to reduce (compress) the dynamic range of the vocal to around 10dB. The vocal can now be placed at around +5dBu. At this level, the dynamic range of the vocal is from 0dBu to +10dBu. The lower level phrases will now be well above the lower level of the mix and louder phrases will not overpower the mix, allowing the vocal to ‘sit in the track’.

The same discussion can be made about any instrument in the mix. Each instrument has it’s place and a good compressor can assist the engineer in the overall blend of each instrument.

This brings our discussion to a another good question…

Does every instrument need compression?

This question may lead many folks to say ‘absolutely not, overcompression is horrible’. That statement can be qualified by defining ‘overcompression’. The term itself, ‘overcompression’ must have been derived from the fact the you can hear the compressor working. A well designed and properly adjusted compressor should not be audible! (Of course this can make a well designed compressor difficult to demonstrate!) Therefore, the overcompressed sound is likely to be an improper adjustment on a particular instrument. Why do the best consoles in the world put compressors on every channel? The answer is simply that most instruments need some form of compression, oftentimes very subtle, to be properly heard in a mix.

Why do you need noise gates?

Consider the compressed vocal example above and you now have a 20dB dynamic range for the vocal channel. Problems arise when there is noise or instruments in the background of the vocal mic that became more audible after the lower end of the dynamic range was raised. (air conditioner, loud drummer, etc.) You might attempt to mute the vocal between phrases in an attempt to remove the unwanted signals, however this would probably end disastrous. A better method is to use a noise gate. The noise gate threshold could be set at the bottom of the dynamic range of the vocal, say -10dBu, such that the gate would ‘close’ out the unwanted signals between the phrases.

If you have ever mixed live you know well the problem cymbals can add to your job by bleeding through your tom mics. As soon as you add some highs to get some snap out of the tom the cymbals come crashing through, placing the horn drivers into a small orbit. Gating those toms so that the cymbals no longer ring through the tom mics will give you an enormous boost in cleaning up the overall mix.

Courtesy Presonus. Used by permission.

Here We Go Again: Congress Expected to Delay Digital Television

Comment: While the FCC and Congress are wrangling about the transition to Digital TV, the future of many of our wireless microphones is at stake. This is the latest piece of news: it looks like the wrangling will succeed this time, and the deadline for the transition that will require us to re-scan all of our mics will be put off from later this month to early summer, but keep in mind: that's only the deadline. The bill as it now stands appears to give individual TV stations the choice of when they make their switch: any time between now and then. Please keep your eyes and ears open. Your region's stations could surprise you! Call, email or Facebook with questions or comments.

February 02, 2009 |

The U.S. House of Representatives is expected to complete congressional action Wednesday on a bill that would delay for four months the nation's conversion from analog to digital television broadcasts. No, this isn't a story from last week that got republished by accident. No, this isn't a joke. Yes, this is Déjà vu all over again.

When we last saw our heroes, the Senate was passing the DTV Delay Act (Monday) and the House was shooting it down (Wednesday). President Barack Obama proposed the delay, so his signature is assured -- if the bill can emerge from the Congress. It got a second chance when the Senate, on Thursday, voted it up again. The House is scheduled to vote on the Senate's version of the bill (S. 352) on Wednesday and this time, it is expected to fall into line.

What changed things? The next House vote will require only a simple majority -- and Democrats control the House by a comfortable margin. Last week's vote required a two-thirds majority, and fell about 20 votes short.

No answer seems to have surfaced on whether this is even a good idea.

Far from giving analog stragglers some breathing room, some experts say delaying the transition will only make matters worse. "No matter when we have this transition, there are going to be people who are not ready for it," Duke professor and former FCC chief economist Leslie Marx told Wired.com before last week's House vote. "I think the best thing for our country is just to go ahead with the transition, and then work hard to get everybody up to speed."

The legislation would, more or less, put on hold what was going to be like the throwing of a big switch on Feb 17: from all analog television signals, to all digital, everywhere for everyone, ready or not. The "readys" with digital tuners would have the benefit of better-looking, better-sounding programming; the "nots" would have snow.

The DTV Delay Bill pushes the date back to June 12, but also allows broadcasters to switch to digital unilaterally, creating the prospect of a patchwork roll out. That peculiarity -- and the notion that delay will do nothing to suddenly inspire a Nielsen-estimated 6 million households to do in the next four months what they haven't bothered to do for the past three years -- killed the bill last week.

The futility issue is only one of the problems with delay. Companies that won auctions for wireless spectrum that is to be freed up on Feb. 17, like AT&T and Verizon, could reasonable seek compensation for not getting the property they were to acquire that day. The Delay bill doesn't address this issue at all.

"Companies have paid $19 billion for the right to use that spectrum, and the wireless communication that could be offered on that spectrum is valuable," said Marx. "If I were one of the companies that purchased spectrum licenses in the FCC's 700-MHz auction, I'd sure be asking the government what kind of compensation I was going to be receiving for, in some sense, the government not providing the good as advertised that I purchased at the auction."

And the average American television station stands to lose $10,000 a month as a result of the proposed delay. They could, under the law, give the FCC 30 days notice and drop analog delivery -- but that could create that confusing patchwork of service and irritate customers who see the Delay bill as, well an actual Delay bill.

Part of the problem could be that the Commerce Department's National Telecommunications and Information Administration spent all $1.34 billion it was allocated to help consumers and businesses make the transition to digital broadcast television, according to InformationWeek, while still not sufficiently preparing the populace for the transition. That allocation included a program to subsidize $40 of the cost of a signal-dumbing converter box that those Americans who still get TV through an antenna (instead of cable or dish) need to see digital programming on analog sets.

But there's even confusion about whether that money has been spent. "The DTV converter coupon program is not out of money; only half of the $1.5 billion in the coupon program has been spent," wrote ranking member of the Committee on Energy and Commerce to House Speaker Nancy Pelosi. It's possible that many of those coupons, which had expiration dates, are sitting around in drawers like those unused rebates we all intended to use right away.

The proposed legislation would pump another $650 million into the program.

Whenever it happens, and whatever the cost, the transition to digital broadcast television will improve over-the-air sound and video quality, enable more channels to be broadcast and free up valuable spectrum for new wireless services.

According to the new acting FCC chairman Michael Copps, a lack of focus on the part of the Bush administration is at fault for this confusing, and likely expensive, situation.

"At this point, we will not have -- we cannot have -- a seamless DTV transition," Copps told the FCC Consumer Advisory Committee on Friday (.pdf). "There is no way to do in the 26 days new leadership has had here what we should have been laser-focused on for 26 months. That time is lost, and it's lost at a cost."

By Eliot Van Buskirk 
From Wired Magazine's blog.

Not So Mysterious: Using Polarity As Another Tool For Optimizing Drum Sound

A method for quickly finding a consistent starting point can help take some of the voodoo out of your system

November 11, 2009, by Dave Rat

It’s pretty common knowledge that if you get the wires mixed up when hooking up two loudspeakers that something “not good” happens.

Loudspeaker phase (actually, polarity) seems at first glance a pretty simple concept. If both loudspeakers are moving outward at the same time the sound adds together, and if one is moving out while the other moves in, the sound cancels out, especially the low frequencies.

Hearing this effect is quite easily demonstrated - listen to your home stereo loudspeakers while standing midway between them and then listen again after reversing the leads on one side. You should notice a very apparent decrease in the lows when they’re wired the wrong way.

To picture why this happens, imagine a very simple pulse or “positive pressure wave”

open drum techniques

being reproduced by both loudspeakers simultaneously. The two positive pressure waves add together and that means addition or “louder.”

Reverse the leads to one of the loudspeakers and one loudspeaker moves outward (toward you, positive pressure) and the other moves inward (away from you, negative pressure).

The pressure wave from one loudspeaker is being “sucked out” by the other loudspeaker, also know as cancellation or “not as loud.”

If we reverse the other loudspeaker lead as well, so that both loudspeakers have reversed leads, both will now move away from you. The two negative pressure waves add together, and that is once again addition or “louder.”

In most situations, it doesn’t much matter whether both loudspeakers move toward or away from you, as long as both are doing the same thing at the same time.

Simple, right?

If it was just loudspeakers, all this would be easy .But things are rarely ever simple in the real world of live audio. There are microphones, amplifiers, instruments, drums and plenty more that also make lots of noise. Add in monitors pointing in various directions, and some interesting things happen.

Everyone Does It (Just About)
Nearly every engineer that uses a snare bottom microphone naturally reverses its polarity. Seems simple enough, and you can hear the added lows and punch when pushing the button next to the word “phase” on the console when both the top and bottom snare mic channels are at similar levels.

Fair enough - drummer hits snare, it’s head moves down/away from the top mic while also moving down/toward the bottom mic. The top mic sees a negative pressure wave and the bottom mic sees a positive pressure wave.

It’s not too much different than our loudspeaker example - negative pressure wave plus positive pressure wave equals cancellation, and for most applications, cancellation equals bad.

The simple solution is to reverse the polarity of either the top or bottom mic to create addition instead of cancellation.

The Way Things Are Supposed To Be
First let me state that a positive pressure on a “pin 2 hot” mic should produce a positive voltage on pin 2 of its XLR output connector.

Assuming you have a properly wired pin 2 hot sound system, that positive voltage on pin 2 will eventually manifest itself as a positive (outward) motion on the loudspeakers in your system. (Yes, I know some JBL stuff will go inward, and there are other exceptions to take into account.)

But why does this matter beyond snare bottom?

Because if you mic the kick from inside the drum (non beater side of the head), then the kick drum beat will produce a positive pressure on it’s mic, and therefore, in most pin 2 hot systems, a positive outward motion of the drum monitor loudspeakers.

Imagine sitting at the drum kit: hit the kick, the head is moving away from you, the drum monitor loudspeaker is moving toward you (negative pressure wave from the kick and positive pressure wave from the drum fill). What do we have? Cancellation, just like in the home stereo with one loudspeaker reversed.

And not only do you have cancellation, but there is another problem as well; the drum head moves away from the drum monitor, the drum monitor loudspeaker moves toward the drum head and pushes the head in a bit farther, and then the reverse happens - the drum head rebounds toward you, while the monitor loudspeaker moves away.

The drum head and monitor loudspeaker are augmenting each others’ motion, creating “resonance” and increasing feedback susceptibility. This is generally not a good thing.

But all you need to do is reverse the kick drum mic polarity, and now the kick drum and drum fill outputs not only add together, but the combination becomes overall less resonant.

Makes Sense… But Does It Really Matter?
If you try this approach, keep in mind that time delay induced by digital processors and drum fill placement can greatly affect audibility.

So to really hear the difference and set the proper polarity, bypass all drum fill and kick channel EQ, and then bring up the kick in the drum fill to the point where it is just on the verge of feedback.

Now, by pressing the phase reverse on the kick channel, you should be able to determine which way is noticeably more stable.

OK, Did That. Now What?
If you did this right and have found a clearly better sounding kick polarity, use it as a starting point to set polarity for the rest of the drum kit.

Working around the rest of the kit, for every mic for the under side of a drum, set the phase the same as you did for the kick. And for every mic for the top or “stick side” of a drum, set the polarity the opposite of how the kick is set.

Keep in mind that this is a starting point - upward facing monitors near a floor tom tend to be more stable with the opposite polarity than this approach dictates.

Polarity is another tool that you can use to achieve the sound you’re seeking. here is no “right” or “wrong” way but having a method for quickly finding a consistent starting point can help take some of the voodoo out of your system.

What About The Cymbals?
Polarity issues are going to have the most noticeable effect on low frequencies, as well as when two sources are reproducing similar signal are in very close proximity to each other or mixed together.

Higher frequencies and things panned hard left and right in the mains will often sound different, but there will not be a definitive “ better” sounding choice.

How far is too far? I personally take it pretty far, and further, follow this same pattern on my house console as well. Both my kick and snare bottom are reversed polarity (I top mic my toms).

But how much of this you employ, is, of course, up to you. What we’re doing here is establishing a clean stating point for you to make decisions to change polarity on specific channels to achieve desired results.

Dave Rat is the co-founder and owner of Rat Sound, a leading sound reinforcement company based in California. Courtesy ProsoundWeb

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