DrawmerUSA - Noise Gate Application Guides

DRAWMER Gates Application Guides

DRAWMER DS201 Dual Channel Frequency Channel Gate
The Drawmer DS201 two channel single rack space gate is a long time industry standard. A gate is used for isolating a particular sound from other sounds present which are present in any live playing situation on stage or in the studio. A gate is functionally a straight wire with a sound activated switch. When the desired sound reaches the gate's input, the switch closes, allowing the sound to pass through unaffected. When the gate is presented with relative silence or low level extraneous sounds at a level lower than expected from the intended source, it remains closed and that undesired sound never reaches the output, improving the definition of your mix. For example, when multiple mics are placed on individual drums in the kit, the snare mic will pick up some sound from nearby drums so it's impossible to get just the snare in the snare channel. By using a gate, the snare mic can be muted until there's a direct hit on that drum, making for a much cleaner snare sound.

The DS201 does its job so well because rather than opening on any sound that's above the minimum amplitude threshold, "Frequency conscious" high and low pass filters allow you to select the frequency range over which the gate opens, and allows the gate to ignore sounds that fall outside that range. By setting the filters around the predominant frequency produced by the kick drum - typically in the 50 to 100 Hz range, even a loud snare or tom won't leak into the kick channel because the gate remains closed until it hears the kick drum.

Intuitively you'd want the gate to open and close as quickly as possible to let through the minimum amount of undesired sound, but having control over the rate at which the gate opens and closes can give you another way of shaping the sound by applying the gate's attack and decay times to the waveform envelope. You can reduce the decay of a sound that sustains too long by carefully setting the hold time to keep the gate open for as long as you want the sound to ring on, then adjusting the decay rate so that you hear a natural decay rather than an abrupt cut-off. Using the fastest attack time assures that the gate doesn't clip off the leading edge of a sound or the first syllable of a word, but by adjusting the attack time, it's possible to re-shape and soften the attack if desired.

An external key input allows another signal to control the gating action. This can be effective in creative ways such as tightening up a bass part to follow the kick drum.

The DS201 can be switched to function as a ducker. In this mode, audio passes straight through unaffected until a signal is received at the external key input. The audio signal will be reduced in level (or completely shut off if desired) as long as an above-threshold key signal is present. This is useful in voiceover applications to drop the level of background music during narration, in broadcast, or as an override in an installed sound system.

Studio Applications:
The most common studio application for a gate is to help separate percussive instruments (typically a drum kit) where each drum has its own microphone. Gating the individual microphone signals reduces or eliminates the muddy sound or comb filtering that occurs when two slightly different versions of the same sound, picked up by two microphones, are mixed.

With careful adjustment of the high and low pass filters and the Threshold control, you can keep each mic turned off except when its source is playing. By engaging the Key Listen switch, instead of the full bandwidth, ungated signal, you'll hear the output of the filter section. By listening to the playing of each source individually, you can adjust the filter to pass the predominant frequency range and reject sounds that you don't want to open the gate. Check the filter setting by playing what's being picked up by an adjacent mic and see that it's adequately rejected. When the proper filter range is located, adjust the Threshold so that the gate opens reliably on the softest sounds from the desired mic, and rejects random noise and rumble that may fall into the filter response bandwidth. Good starting points for the filters are 35 to 250 Hz for a kick drum and 1 to 2 kHz for a snare.

The Attack, Hold, and Decay controls adjust the response times of the gate. Attack sets the slope of gate opening, from an essentially instantaneous 10 microseconds to a gradual one second. Fast attack times assure that the input isn't clipped off, but too rapid an attack time on a fast transient can result in generating a click when the gate opens. Increasing attack time will eliminate these gate-induced clicks. A longer attack time can be used to modify the attack of the signal, softening something that's too hard, or even providing a gentle swell to make a sound "bloom".

The Hold control adjusts the length of time the gate remains fully open after the signal drops below threshold. You'll want to use a short hold time for transient sounds such as drums, matching the hold time to the natural decay of the sound. For speech, allowing the gate to close between words or phrases can sound disconcerting because the background noise jumps up and down, so lengthen the hold time so that the gate remains open long enough to carry the signal through natural pauses in speech. The Decay control adjusts the slope of the gate closing, from a rapid 5 ms to a gradual 4 second fadeout. All of the dynamics controls should be set by ear but good starting points for drums are 0.1 ms for Attack, and 50 ms Hold and Decay.

The Range control adjusts how much attenuation the gate provides when it's off. Often gating a microphone signal completely off doesn't sound natural since not only the desired signal, but all the ambience goes away. By raising the Range, you can allow low level ambient sound to pass through all the time so you don't hear background noise "pumping" when the gate opens and closes. In most mixing situations, attenuating a nearby mic by 20 dB is sufficient to prevent comb filtering and muddiness while preserving some ambient sound and spaciousness.

Typically a gate is triggered by its own input signal, but on occasion you may with to trigger it from a different source. If the bass isn't right together with the kick drum, gate the bass and set the gate key input to External. Connect the rear panel Key jack to the kick drum signal and now the gate will open on each beat of the kick drum. If the bass player is a bit early, the gate will hold him off until the drummer hits the kick. Since the kick drum drops below threshold quickly and you'd like some sustain on the bass, use the Hold and Decay controls for a natural sounding decay. Another useful trick with the external key input is to use the kick drum to key an oscillator set at around 100 Hz. Mix the oscillator in with the kick drum for a really deep sound.

The Stereo Link switch allows the two gates to key off the same signal. When the Stereo switch is engaged, the gate is derived from the left channel only. This mode is useful when gating a true stereo source. The stereo link function can be used with two different signals in a manner similar to the external key input to tighten up a bass with the kick drum. With the kick in the left channel and the bass in the right channel, stereo linking will allow the bass gating to follow the kick without patching. Try this technique, too, to synchronize a background singer who's a little ragged. Link the channels using the master (left) channel to gate the best singer and the slave channel to gate the ragged singer. She'll be there to add harmony but won't come in too early or hang on too late.

Live Sound:
Gates are an essential part of a modern live sound system. Concert riders often specify multiple gates and the Drawmer DS series will make any touring engineer feel at home. The most common live sound application for gating is to help separate instruments in the drum kit when each drum is close-miked. By gating each microphone, you can reduce the muddy sound that results when mixing nearly the same signal picked up by two mics intended for separate drums.

The Drawmer Frequency Conscious gates are particularly well suited for this application since it's easy to tune the gate to focus on gating a set of drum mics based on the drum's frequency range, 50 Hz for the kick drum, 100 Hz for floor toms, 1-2 kHz for the snare etc. By using the Key Listen switch and soloing channels, you can easily zero in on the dominant frequency for gating.

Often gates are used on vocal mics to eliminate bleed from the stage sound when there's no one singing. For this application, wider band or even full band rather than band-limited keying is usually preferred. If you find that the gate is opening on drum hits, set the low cut filter to cut just below the vocal range, around 250 Hz, to prevent keying on low frequencies. Set the high cut filter high enough so that keying is reliable for the singer, usually 5 kHz or above. While short attack, hold, and release times are appropriate for drums, vocals usually work best with slightly longer attack time, around 1 ms, with the hold time adjusted so that the gate doesn't close between words or phrases. Generally vocal mics sound more natural when not gated completely off since this makes too drastic a change in the ambient sound. Try setting the Range for around 20 dB of gating.

It's difficult to eliminate buzz and other stray noises from an instrument amplifier or direct pickup when on stage. Lighting cables and electric machinery are notorious noise radiators. A gate applied to an electric guitar or bass can eliminate buzz when the instrument isn't being played. Drawmer gates work equally well as part of the player's processing rack (so he sends a gated signal to the mixing console) or patched into the instrument's channel through the console's channel insert connections.

Consider using a DS gate set up as a ducker on the console channels carrying the recorded intermission music, with keying coming from the MC's microphone. If someone makes an announcement during intermission while you're away from the console, he won't have to fight the recorded music. It will drop down in level when he starts talking, just as if you were there.

Installed Sound Applications:
A common installed sound application for gates is when several microphones are arranged around a conference or speaker's table. Since the potential for feedback increase with the number of open microphones, by turning mics off that aren't being spoken into, feedback and background noise are reduced. In this application, hard gating is usually not desirable. To avoid the jarring "total silence" when no one is speaking, set the Range control for a 20 dB drop rather than total gating.

A DS201 set up in the ducking mode can be used in a background music system with paging. Keying the ducker from the paging microphone signal will reduce the level of the background music while speaking, and return it to normal level after the page. The Drawmer 1962 mic preamp and processor includes a mixer to combine the mic signal with an external input. Add background music with a DS201keyed from the microphone signal and you have a basic background system with paging in two compact boxes.

DRAWMER DS501 Dual Frequency Conscious Gate with Peak Punch

The Drawmer DS501 two channel single rack space gate is an advanced version of the long time industry standard Drawmer DS201 with an added feature called Peak Punch.

A gate is used for isolating a particular sound from other sounds present which are present in any live playing situation on stage or in the studio. A gate is functionally a straight wire with a sound activated switch. When the desired sound reaches the gate's input, the switch closes, allowing the sound to pass through unaffected. When the gate is presented with relative silence or low level extraneous sounds at a level lower than expected from the intended source, it remains closed and that undesired sound never reaches the output, improving the definition of your mix. For example, when multiple mics are placed on individual drums in the kit, the snare mic will pick up some sound from nearby drums so it's impossible to get just the snare in the snare channel. By using a gate, the snare mic can be muted until there's a direct hit on that drum, making for a much cleaner snare sound.

While the Drawmer gates are among the fastest responding gates in the industry, it still takes a finite amount of time for the sound level to reach the threshold at which the gate will open. When attempting to eliminate a high surrounding noise level, it's possible to gate out the steep initial portion of a sharp transient, for example, the attack of a kick drum. The initial attack is necessary to give the sound its punch and determines how loud it sounds in the mix. If the attack is softened, it's often necessary to run the level of the kick too high in the mix in order for it to be audible, robbing useful spectrum space. The Peak Punch circuit in the DS501 restores the attack by adding a gain boost for a very short period of time when the gate initially opens. We perceive the kick to be louder even though we've actually added very little energy by restoring the initial transient.

The DS501 does its job so well because rather than opening on any sound that's above the minimum amplitude threshold, "Frequency conscious" high and low pass filters allow you to select the frequency range over which the gate opens, and allows the gate to ignore sounds that fall outside that range. By setting the filters around the predominant frequency produced by the kick drum - typically in the 50 to 100 Hz range, even a loud snare or tom won't leak into the kick channel because the gate remains closed until it hears the kick drum.

An external key input allows another signal to control the gating action. This can be effective in creative ways such as tightening up a bass part to follow the kick drum.

The DS501 can be switched to function as a ducker. In this mode, audio passes straight through unaffected until a signal is received at the external key input. The audio signal will be reduced in level (or completely shut off if desired) as long as an above-threshold key signal is present. This is useful in voiceover applications to drop the level of background music during narration, in broadcast, or as an override in an installed sound system.

The DS501 provides a Peak Punch circuit which can be engaged after setting the basic gate operation. This is a dynamic feature that adds up to 12 dB of gain for the first 10 ms after the gate opens. The Level control is used to adjust the amount of "punch", while, with the Peak Punch filter engaged, the Tune control adjusts the frequency range that's accentuated. Low frequencies add depth, while tuning to a high frequency can add a sharp "rim shot" kind of sound to a snare drum. In the Full band position of the Peak Punch switch, the full frequency range is accentuated and only the Level control is active.

Live Sound Applications:
Gates are an essential part of a modern live sound system. Concert riders often specify multiple gates and the Drawmer DS series will make any touring engineer feel at home. The most common live sound application for gating is to help separate instruments in the drum kit when each drum is close-miked. By gating each microphone, you can reduce the muddy sound that results when mixing nearly the same signal picked up by two mics intended for separate drums.

Consider using a gate set up as a ducker on the console channels carrying the recorded intermission music, with keying coming from the MC's microphone. If someone makes an announcement during intermission while you're away from the console, he won't have to fight the recorded music. It will drop down in level when he starts talking, just as if you were there.

A DS501 set up in the ducking mode can be used in a background music system with paging. Keying the ducker from the paging microphone signal will reduce the level of the background music while speaking, and return it to normal level after the page. The Drawmer 1962 mic preamp and processor includes a mixer to combine the mic signal with an external input. Add background music with a DS501keyed from the microphone signal and you have a basic background system with paging in two compact boxes .

DRAWMER DS404 Four Channel Frequency Conscious Gate
The DS404 is a four-channel gate in a single rack space, ideal for systems where many inputs are gated and rack space is limited. What's missing to pack double the gating into the same space? The envelope dynamics controls are streamlined. The Hold and Decay functions are combined into a single Release control, and Attack control is replaced with a single Hard/Soft gating switch, and the Range control is replaced by a two-position switch. While the DS404 doesn't offer the wide range of envelope control of the other models, it's quick to set and has preset responses appropriate for both rapid drum gating and softer action more appropriate to vocals or guitars. Of course being a Drawmer, it has the Frequency Conscious gating.

A single Hard/Soft switch selects between two sets of attack, release, and hold times. The Hard position is essentially instant-on and instant-off, and works best with drums and other highly percussive sounds. A gate action like that might cut off the trailing edge of a decaying sound or the last syllable of a vocal phrase, so the Soft setting is provided which is more like a very fast 'turn up' and 'turn down' function. This prevents clipping of trailing edges and gives smoother action on instruments such as horns or electric guitars that don't have a steep wave front.

The Range switch sets how much attenuation the gate provides when it's off. Often gating a microphone signal completely off doesn't sound natural since not only the desired signal, but all the ambience goes away. By setting the Range so the gate doesn't go completely off, you can allow low level ambient sound to pass through all the time so you don't hear background noise "pumping" when the gate opens and closes. In most mixing situations, attenuating a nearby mic by 20 dB is sufficient to prevent comb filtering and muddiness while preserving some ambient sound and spaciousness. On the DS404, the Range can be selected between 20 dB and 80 dB of attenuation when the gate is closed.

The linking in the DS404 allows you to control the gating of up to all four channels. Pressing the Slave switch on any channel makes it the master for the channel immediately to its right. Pressing the Slave switch on Channel 1 makes its keying controls active on Channel 2 also, while disabling Channel 2's controls. Pressing all of the Slave switches makes the Channel 1 signal key all of the channels. The link function can be used in a manner similar to the external key input to tighten up a bass with the kick drum. With the kick and bass in adjacent channels, linking the two will allow the bass gating to follow the kick without patching. Try this technique, too, to synchronize background singers who are little ragged. Link the channels and put the singer with the best timing through the leftmost channel with the rest of the singers on the other channels. They'll be there to add harmony but won't come in too early or hang on too late.

Live Sound Applications:
Gates are an essential part of a modern live sound system. Concert riders often specify multiple gates and the Drawmer DS404 will make any touring engineer feel at home. It's intuitive and its switchable Range makes it easy to set up for either "hard" or "soft" gating - and it's a Drawmer. The most common live sound application for gating is to help separate instruments in the drum kit when each drum is close-miked. By gating each microphone, you can reduce the muddy sound that results when mixing nearly the same signal picked up by two mics intended for separate drums.

A DS404 in the ducking mode can be used in a background music system with paging. Keying the ducker from the paging microphone signal will reduce the level of the background music while speaking, and return it to normal level after the page. The Drawmer 1962 mic preamp and processor includes a mixer to combine the mic signal with an external input. Add background music with a DS404 keyed from the microphone signal and you have a basic background system with paging in two compact boxes.