DrawmerUSA - Compressor Application Guides

DRAWMER Compressor-Limiters Application Guides

DRAWMER DL241 Two channel Gate and Auto/Manual Compressor-Limiter
The DL241 is a complete stereo or dual mono dynamics package in a single rack space. In addition to a compressor, each channel contains an expander/gate and a peak limiter. The DL241 combines both the action of a traditional ratio-above-threshold compressor and a soft-knee compressor where the amount of gain reduction progresses smoothly from none (unity gain) to the set gain reduction ratio over about a 10 dB range of input level. This variable ratio characteristic gives outstanding results in a wide range of applications.

The DL241 has the familiar Threshold, Ratio, Attack, Release, and Gain makeup controls. The Ratio is the fixed compression ratio reached at the end of the soft knee curve of increasing gain reduction. The point at which soft knee gain reduction begins is set with the Threshold control. Gain reduction increases smoothly for approximately the next 10 dB of input level, at which point the fixed ratio takes over and gain reduction continues at that level.

Attack time is adjustable from 0.5 to 100 ms, Release time can be set in the range of 0.05 to 5 seconds. An Auto button disables the Attack and Release controls and continually optimizes the attack and release times to suit the dynamics of the signal being processed. The Auto setting is a great place to start, and many engineers who are otherwise tweakers keep this mode engaged all the time since it can adapt quickly to changing program dynamics.

One of the problems with using a compressor, particularly in a live sound environment, is that during quiet passages, gain reduction is low (the system or channel gain is maximum), resulting in a rise in background noise or, in worst case, feedback howl. A slow release time sometimes can help in this situation, but often the solution is to add an expander or gate ahead of the compressor so that low level background noise doesn't appear at the compressor input. This isn't always satisfactory since it's possible to gate out softly spoken or sung words entirely or chop off syllables. The DL241 uses a Program Adaptive expander circuit or "soft gate" which varies its ratio depending on the dynamics of the input signal. Low level signals receive little attenuation while background noise is attenuated to a greater extent.

The final stage before the compressor output is a very fast acting peak limiter that sets the maximum level of the output. To avoid an obvious clipping sound from continuous limiting, when limiting occurs for longer than 20 ms before the peak drops below the limiter threshold, additional pre-limiter gain reduction kicks in with a release time of approximately 1 second. Normally the compressor gain reduction and output gain should be set so that the peak limiter operates rarely if at all. It's there for protection of the system and avoiding digital "overs."

A Stereo Link switch applies the controls of the left channel to both channels so that a stereo signal can be compressed without image shifting if the balance between the channels changes.

The DL241 is available in two models which are identical other than the type of input and output connectors used. One model has XLRs, the other ¼" TRS jacks. Both models are equipped with a switch to select nominal operating level of -10 dBV or +4 dBu to accommodate pro or semi-pro systems or the reduced level channel insert points found on many consoles.

Studio Applications:
In the studio, the DL241 is normally connected to a channel through the insert send and return points. Since it will accommodate both balanced and unbalanced connections at either -10 dBV or +4 dBu nominal levels, it's easy to interface to just about any console. Alternately, the DL241 can follow a mic preamp and be connected directly to the recorder input.

Initial setup is best accomplished with the Expander off and the Peak Limiter threshold set to maximum. This allows you to listen to only the compressor action. Once the compression is set for the desired action on normal program material, the Expander and Limiter can be applied to take care of abnormalities. With the Attack and Release controls set to Auto, simply adjust the Threshold for the desired amount of gain reduction.

Once you have the desired amount of gain reduction, you may wish to turn the Auto function off and fine tune the Attack and Release times manually. A slow attack will allow initial transients to get through before gain reduction begins to take place. This is effective on basses, drums, and plucked or percussive instruments. A slower attack time will avoid the tendency for a compressor to reduce brightness since it will let the leading edge of bright sounds pass through unaffected. A faster attack time causes gain reduction to begin sooner and is often useful on vocals. An attack time that's too fast for the source may cause clicks, so that's the time to slow it down. Use a release time that's slow enough to carry gain reduction over phrases to avoid "pumping".

Now the Expander can be set. For all sources but sharp, percussive sounds, the longer release time is probably the best setting, but try both. Find a section of the program material that contains pauses and adjust the threshold of the Expander as low as possible while still attenuating the noise during the pauses. In the studio, the expander can be helpful in keeping headphone leakage from creeping on to the track when the singer is between verses.

When the compressor is working to your satisfaction, use the Gain control to bring the output level of the DL241 back to normal for the channel. Once the gain setting is correct, the Peak Limiter threshold can be set so that the limiter LED only lights on occasional peaks.

To use the DL241 on a stereo source, engage the Stereo Link switch. This disables the controls on the right channel and both channels are affected by the left channel controls.

When compression, peak limiting, and stereo linking are combined, the DL241 makes a great mastering tool. With independent controls for compression and limiting, you can easily adjust the peak-to-average ratio of the program material, which corresponds to perceived loudness. A good starting point is with the compressor threshold set at 0 dB and the peak limiter set to +10 dBu, adjusting the gain so that the limiter LED flashes on occasional peaks. Adjusting the compression ratio will change the apparent loudness. Since the limiter puts a cap on the maximum output level, set the input gain on the master recorder so that peaks are just below full scale and you'll get maximum loudness without fear of digital "overs".

Live Sound:
In live sound, quick setup is important. The straightforward controls and pushbutton selection of automatic, program dependent attack and release makes it easy to get a source to sit properly in a live mix.

The DL241 is available with either XLR or ¼" TRS jacks for input and output for flexible connections to any system. Regardless of the jack type, both are balanced and both are selectable for -10 dBV or +4 dBu operating levels. For connection to unbalanced equipment such as console channel inserts, a ¼" TS plug will work fine.

The DL241 can be used in an instrument processing rack, however it lacks a very high impedance input suitable for direct connection to an instrument pickup. For this application, use a good instrument preamp first (a Drawmer 1962 would be a great choice), followed by the DL241. If you have a keyboard rig with several keyboards going into an on-stage mixer, the DL241 on the mixer output that feeds the house sound system will give you an extra degree of control over your mix.

Installed Sound Applications:
In an installed system, you're usually looking for a set-and-forget processor since there is often no mix engineer or attendant to make adjustments. A gated compressor is a useful component in such a system.

By gating the input to the power amplifiers, you avoid annoying amplification of low level background noises such as air handlers or people speaking off mic and not addressing the intended audience. Set the gate threshold so that the ambient noise is gated off, then make sure the threshold is low enough to open the gate when someone steps up to the microphone to speak. The choice of fast or slow release time is dependent on the program material, the level of the ambient noise you want to gate, and the acoustics of the room. Experiment to see which works better in your situation.

The compressor will help even out the differences between loud and soft speaking voices. A compression ratio somewhere between 3:1 and 6:1 and automatic attack and release will handle a fairly wide range of speaking or singing voices. The peak limiter is a good safety valve should something go astray. Most installed sound systems today use balanced XLR connections at +4 dBu operating level, so that's probably the model you'll want to choose. For compatibility with other equipment, the DL241 is available with ¼" TRS jacks, with a selection of +4 dBu or -10 dBV operating levels for either connector.

DRAWMER DL441 Four Channel Single Rack Space Compressor-Limiter

The DL441 offers 4 channels of compression and peak limiting in a single rack space. The DL441uses the same basic compression circuitry as the DL241 and has much the same sound, however to pack more compressors into the same space, we eliminated the gate, and attack and release are automatic and program dependent with no individual controls for these parameters.

A unique feature of the DL441 is the Hard/Soft Knee switch. While other Drawmer compressors gradually transition from soft knee action slightly below threshold to hard knee action several dB above threshold, the DL441 allows control over which type of compression action you get. With soft knee action, the compression ratio over much of the operating range is less than what you've set on the knob, but the ratio changes with the signal level. This gives a very smooth and almost undetectable action. Sometimes, though, you want to hear a compressor working because this can be a useful and creative effect. By selecting the Hard Knee setting, below threshold there is no compression action. Once the threshold is reached, however, the compression ratio is what the knob says it is.

Each channel includes a "brick wall" limiter to protect things downstream from overloading. For stereo or multi-channel operation, each channel can be linked to the one to its immediate left, with the controls of the leftmost linked channel setting the threshold, ratio, output level and peak limit for each of the other linked channels.

Inputs and outputs are on XLR connectors, with a switch to select the nominal operating level of +4 dBu or -10 dBV to properly match the threshold to the system operating level.

Studio Applications:
In the studio, the program dependent attack and release times together with the choice of hard or soft knee compression makes the DL441 a deceptively simple yet powerful compressor. Most studio applications will call for the DL441 to be patched in line with a single program source, either by using console channel inserts or between a mic preamp and recorder for tracking or between the recorder output and console line input for mixing.

For a vocalist with fairly good control, soft knee compression with a ratio of between 2:1 and 6:1 will usually do the trick. Adjust the Threshold so that the LED bargraph Gain Reduction meter shows an "eyeball average" of around 3 dB of compression most of the time. For a singer with a less controlled voice, you may want to raise the compression ratio and lower the threshold so that you get around 10 dB of compression on the loudest peaks. Since the average compression is around 3 dB, adding about 3 dB of gain will bring the channel back to normal operating level.

For a pumping kick drum reminiscent of the classic dbx 160 sound, select the hard knee mode, try a ratio of around 10:1 and set the Threshold so that the gain reduction meter indicates 10 to 15 dB of compression most of the time.

The peak limiter follows the compressor, and it should be set so that its LED indicator almost never flashes. If the limiter is working much of the time, this will affect the sound of the compressor. It might be an effect you like occasionally, but it's not the normal way to use this limiter. The Bypass switch is a hard bypass, connecting input to output, so you can easily compare the compressed signal with its uncompressed version.

When working with a pair of channels, for instance a stereo bus or a pair of overhead or room mics when tracking drums, it's important that the compressor affect both channels equally. Pressing the Link switch on a channel couples the channel to the one immediately to its left, making the channel to the left the master for the pair. Use that master controls to set up equal compression for both channels. Generally when used in this mode, soft knee compression works best because it's less noticeable.

When compression, peak limiting, and stereo linking are combined, the DL441 makes a great mastering tool. With independent controls for compression and limiting, you can easily adjust the peak-to-average ratio of the program material, which corresponds to perceived loudness. A good starting point is with the compressor threshold set at 0 dB in the soft knee mode and the peak limiter set to +10 dBu, adjusting the gain so that the limiter LED flashes on occasional peaks. Adjusting the compression ratio will change the apparent loudness. Since the limiter puts a cap on the maximum output level, set the input gain on the master recorder so that peaks are just below full scale and you'll get maximum loudness without fear of digital "overs."

Live Sound Applications:
A DL441 or two in a processing rack would make any live sound engineer happy. It provides both the classic Drawmer sound and the classic dbx sound with four channels in a single rack space. The automatic program dependent attack and release means you'll have time to worry about other things than tweaking the compressor. Patch it into individual channels, adjust the ratio and threshold for the sound you want, trim up the gain and you're good to go.

In general, select soft knee for things where you don't really want to hear the compressor working such as vocals or guitars, and select hard knee when you want to use the compressor as an effect as well as to control levels.

A pair of linked channels on a stereo PA mix with compression set for a fairly low ratio of 1.5 to 3:1 and threshold set so that compression just begins (around 1 to 2 dB ) on normal program material is a good way to protect the system and the audience's ears. Set the Gain so that the output level meter rarely goes above +5 dB, and set the peak limiter at +15 dB. This will give you around 20 dB of headroom to work with in your mix, while keeping allowing 10 dB of headroom for the system. Loud things can get louder, and your system will stay clean.

A rack full of compressors can be very useful for monitor mixing. Try dedicating a DL441 to the drummer's monitor mix, using three channels for the kick, snare, and toms submix, and the fourth channel for something melodic like bass, keyboards, or vocals. With the DL441 riding gain, he'll always be able to hear his drums and whatever he needs as a cue.

If your live sound business involves rentals, the DL441 is an excellent addition to a general purpose house or monitor processing rack. It's compact, quick and easy to set up, and it's a sound that's well known and well respected.

Installed Sound Applications:
In a conference room or a house of worship, there's often the situation where several people need to speak from different positions, some are experienced speakers, others shy away from the mic.

Setting up a channel of DL441 on each microphone channel with the threshold around -10 dB and ratio of 6 to10:1, there will be enough gain for the timid and enough gain reduction for the bold speaker. Since the compressor will be working fairly hard on a loud source, the peak limiter can be set a bit lower than normal, around +10 dB. Set the gain so that a quiet speaker reaches an output level of around -5 dB and the speaker with the full booming voice won't startle the listeners.

DRAWMER DL251 Two Channel Spectral Compressor
A problem that sometimes occurs when using compression is an apparent dulling of the highs due to the fact that the waveform envelope is modified by the compressor's attack characteristic. The DL251 incorporates a unique Dynamic Spectral Enhancement circuit which expands the high frequencies when compression is active, restoring the high frequency definition that is sometimes reduced in the process of compressing dynamics. It's particularly effective on vocals where clarity is often defined by content in the mid-high frequency range. It also helps to maintain clarity of transients in harmonically rich sources such as slap bass.

The basic compressor section of the DL251 works just like the DL241, including the choice between automatic and manual attack and release settings and hard or soft knee characteristic for the onset of gain reduction. The DL251 doesn't have the expander/gate of the DL241, however there are some additional features.

A side chain insert jack provides a patch point for connecting an equalizer into the compressor's detector path, allowing frequency dependent gain reduction. Typically a high frequency boost here is used to reduce sibilance (de-essing). Similarly, a low frequency cut will raise the compressor's threshold at low frequencies, allowing the "whomp" of a bass drum to pass through without reducing the level of the rest of the program material.

To go along with this rear panel jack, a front panel Side Chain (S/C) Listen switch routes the output of the inserted equalizer to the compressor output to aid in identifying problem frequencies that need more or less compression.

A rear panel switch selects peak or average response for the stereo link function. In the Peak mode, whichever channel has the loudest level will control the gain reduction in both channels. In the Average mode, the signal level of both channels is averaged and the average level of the channels is used to control the gain of both.

Then there's the Enhance control. This increases transient detail when compression is applied. The amount of enhancement is proportional to both the setting of the control and the amount of compression taking place. This is an adjust-by-ear-to-taste control which demands experimentation.

Inputs and outputs are balanced XLR connectors with the operating level switchable between -10 dBV and +4 dBu.
The sidechain insert jacks are unbalanced on ¼" TRS jacks with send on the ring and return on the tip.

Studio Applications:
In the studio, the DL251 typically connected to a channel through the insert send and return points. Since it will accommodate both balanced and unbalanced connections at either -10 dBV or +4 dBu nominal levels, it's easy to interface to just about any console. Alternately, the DL251 can follow a mic preamp and be connected directly to the recorder input.

Initial setup is best accomplished with the Peak Limiter threshold set to maximum and the Enhance function off. This allows you to listen to only the compressor action. Once the compression is set for the desired action on normal program material, the Enhance and Limiter can be applied to take care of abnormalities. With the Attack and Release controls set to Auto, simply adjust the Threshold for the desired amount of gain reduction.

Now the Enhance can be engaged and adjusted. The Enhance only works when the compressor is over threshold and gain reduction is actually taking place. Turning the control clockwise increases the amount of enhancement, and the green LED shows the degree of enhancement on an instantaneous basis. Since Enhance effectively restores the transient detail lost when using a fast attack time, you can consider these two controls to be interactive. If the dynamics calls for a fast attack, but you don't like what that setting does to the high frequency detail, the Enhance control can be used to restore what the fast attack has taken away.

The Enhance function can also be used to create special effects by deliberately over-enhancing the transient detail of a signal. Since Enhance is related to the amount of gain reduction taking place at any time, setting a long release time will increase the amount of time that Enhance remains active. Typical applications are adding extra brightness to a steel string acoustic guitar or tine piano without simply boosting highs as an equalizer does. Care must be taken with vocals so as not to over-emphasize sibilance unless this is desired for creative reasons.

When the compressor adjusted for the amount of dynamics control you desire, use the Gain control to bring the output level back to normal for the channel. Once the gain setting is correct, the Peak Limiter threshold can be set so that the limiter LED only lights on occasional peaks.

If the DL251 is being used on a stereo source, engage the Stereo Link switch. This disables the controls on the right channel and both channels are affected by only the left channel controls. When used across a full stereo mix, the Average setting for the stereo link will usually be preferred. Peak linking mode may be work better if the DL251 is used across a bus pair with a lot of transients, such as a drum submix. Note that if an equalizer is patched to the sidechain insert, setting the equalizer patched into the left channel affects the compression on both channels.

When compression, peak limiting, and stereo linking are combined, the DL451 makes a great mastering tool. With independent controls for compression and limiting, you can easily adjust the peak-to-average ratio of the program material, which corresponds to perceived loudness. A good starting point is with the compressor threshold set at 0 dB in the soft knee mode and the peak limiter set to +10 dBu, adjusting the gain so that the limiter LED flashes on occasional peaks. Adjusting the compression ratio will change the apparent loudness, and add a little extra sparkle with the Enhance circuitry. Since the limiter puts a cap on the maximum output level, set the input gain on the master recorder so that peaks are just below full scale and you'll get maximum loudness without fear of digital "overs".

The DL251 can be used in an instrument processing rack, however it lacks a very high impedance input suitable for direct connection to an instrument pickup. For this application, use a good instrument preamp first (a Drawmer 1962 would be a great choice), followed by the DL251. The Enhance function can add another dimension of control to guitars and electronic keyboards. .

Installed Sound Applications:
In an installed system, you're usually looking for a set-and-forget processor since there is often no mix engineer or attendant to make adjustments.

The DL251 is well suited to broadcast applications either on the announcer's mic channel or on the overall stereo signal going to the transmitter. Compression can improve overall loudness, while the peak limiter will keep modulation within legal limits. The Dynamic Spectral Enhancement can be used to add extra brightness and sparkle to the signal without excessive boost which would necessitate lower average levels or excessive peak limiting.

DRAWMER Six-Pack Six Channel Compressor/Limiter

If you've come this far, we assume you already know what a compressor is. If not, check out the DL241, then come back and read about this combo. The Six-Pack is a three rack space unit that incorporates six channels of compression that are not only linkable, but linkable in some clever ways which provide dynamics control in any multi-channel format from stereo to 5.1 surround as well as six independent mono channels. Each of the six modules is derived from the famous Drawmer DL241, comprising fully adjustable compressors with threshold, compression ratio, and gain controls with a switchable Auto attack/release/hold mode for quick setup. Like the DL241, there's an adjustable expander/gate ahead of the compressor section and a zero-overshoot peak limiter following the compressor. And like the DL241, the compressor has a soft knee characteristic for the first 10 dB of gain reduction, switching to hard-knee or straight slop at the set compression ratio beyond 10 dB of gain reduction. Each channel has a hard-wire bypass switch. For surround mixing, Channel 6 has a rear panel switch that engages a 120 Hz 24 dB/octave low pass filter to keep anything out of the LFE channel that doesn't belong there.

Studio Applications:
In the studio, the Six-Pack makes an excellent tracking or mixdown compressor by connecting it to a channel through the insert send and return points. Since it will accommodate both balanced and unbalanced connections at either -10 dBV or +4 dBu nominal levels, it's easy to interface to just about any console. Alternately, the Six-Pack compressors can follow a mic preamp and be connected directly to the recorder input for tracking or patched between a multitrack recorder track output and console tape return.

When the compressor is working to your satisfaction, use the Gain control to bring the output level back to normal for the channel. Once the gain setting is correct, the Peak Limiter threshold can be set so that the limiter LED only lights on occasional peaks.

Each channel with the exception of Channel 1 has a Link switch. Pressing that switch links the channel to its neighbor to the left. When linked, the controls on the linked channel become inactive, and that channel is controlled by the channel to its left, or the leftmost channel if more than two channels are linked. Thus you can link all six channels to control dynamics of a 5.1 surround mix, you can have three stereo compressors, or two LCR compressors.

When compression, peak limiting, and linking are combined, the Six-Pack makes a great mastering tool. With its flexible linking, it works equally well using two channels on a stereo mix or a 5.1 surround master. With independent controls for compression and limiting, you can easily adjust the peak-to-average ratio of the program material, which corresponds to perceived loudness. A good starting point is with the compressor threshold set at 0 dB and the peak limiter set to +10 dBu, adjusting the gain so that the limiter LED flashes on occasional peaks. Adjusting the compression ratio will change the apparent loudness. Since the limiter puts a cap on the maximum output level, set the input gain on the master recorder so that peaks are just below full scale and you'll get maximum loudness without fear of digital "overs."

When mastering for surround, by engaging the rear panel LFE filter switch, you can assure that there is no information above 120 Hz appearing in the LFE channel.

Live Sound Applications:
In live sound, quick setup is important. The straightforward controls and pushbutton selection of automatic, program dependent attack and release makes it easy to get a source to sit properly in a live mix. In addition, the compact size and vertical layout makes it easy to adjust quickly in the often cramped and poorly lighted mixing positions.

The program-adaptive expander/gate is ideal for keeping monitor and backline leakage out of the vocal mics when the singers aren't singing, or silencing a noisy stomp box or buzzy guitar or bass when things get quiet on stage. The Six-Pack is also effective when used on a full mix to keep volume from creeping up, and when linked, the peak limiter provides protection for drivers when something unexpected happens on stage. Since the six compressors can be linked together, they can be used to handle the level chores for a multi-zone system so that the apparent source won't wander to fill speakers when the feed to the main speakers goes into compression or limiting.

The Six-Pack is a good addition to a rental rack. It offers the same capability and sound as three Drawmer DL241 compressors in the same amount of rack space, but with what many live sound engineers find to be a more convenient control layout and panel color scheme when working in tight quarters. And it costs less, too.

Installed Sound Applications:
The Six-Pack is ideal for any large installed system with multiple sources that need individual gain and dynamics control. In an installation such as a large house of worship, there will multiple and essentially unattended sources - a microphone at the pulpit, choir mics, a few wireless mics, and perhaps a recorded music source, Each has its own dynamics processing requirements, and the Six-Pack puts full adjustability at the installer's fingertips.