A cure for compression confusion is here. Quit guessing and anguishing over proper compressor and gate settings. Get on with what is important, your work. Rane has created a compressor gate using high quality log rms detectors and Voltage Controlled Amplifiers (VCAs). The DC22S combines quality compression and gate functions with simplicity. No more compression headache!
Lets start with what a compressor actually does. No matter how you cut it, this is an automatic volume control... a hand on a control, turning it down and turning it up again. The hand is fast and accurate, but it is just turning a volume control.
When the input signal reaches a level set by the Threshold control, the compressor begins to turn the signal down by an amount determined by the Ratio control. The DC22S, like most compressors, operates by making the loud signals quieter, but does not make the quiet parts louder. However, by keeping the loud signals under control, the entire system may be turned up when necessary to make the quiet parts louder.
There is more than just a stereo compressor working here. The adjustable Gate is a downward expander, acting like a compressor running in reverse, making the quiet parts quieter. This is valuable in reducing system background noise. The Ratio is fixed at 2:1. When the signal drops below the set Threshold, the Gate Threshold indicator lights and the output level is reduced by 2 dB for every 1 dB the input signal level drops.
When using the DC22S as a true stereo processor with left and right signals, activate the Link switch. In Link mode, channel 1 becomes the Master and channel 2 the Slave. Gate Threshold, Compression Threshold, Compression Ratio and Output Level are all controlled by channel 1. This ensures that both channels track perfectly, maintaining perfect balance and image. The channels are totally independent with the Link switch off.
The DC22S offers performance and simplicity not found (until now) in this price range. Designed for the working musician or club system, The DC22S provides reduced complexity without compromise in audio quality or dependability.
TWO CHANNEL COMPRESSOR / LIMITER
In this case, the audio path on Channel 1 is completely separate from Channel 2, allowing you to use it as a stereo unit or for doing two completely different processes to two completely different signals. For stereo use, the front panel LINK switch allows you to link Channels. When either Channel’s Threshold is reached, both channels compress equally, preserving the stereo image. Channel 1’s Threshold and Ratio settings will affect both Channels.
GUITAR & BASS
Where does the unit go in the signal chain? Well, that depends on how you want it to function. If it’s a compressor / limiter for the input signal, it would go after the guitar (if the guitar has a line-level output) and before the preamp. If it’s to function as a limiter to protect the speakers in the rig, it would go after the preamp and before the power amp. Another method is to insert the unit in the effect loop of the preamp. This allows the bass signal to be affected by the pre-amp first, then the comp/limiter, and then sent to the power amp. This can be desirable with tube pre-amps.
Use it on bass guitar, piano, drums, or vocals—as an effect or to tailor dynamic range for a particular recording medium. Patch it between line-level devices or in your mixer inserts or “loops”. The DC22S gives you more control and a less tortured sound, and keeps instruments sounding “up-front.” In digital recording, compress an extremely wide dynamic range into a signal that won’t go into digital overload, i.e. severe clipping. This is really valuable during a live digital recording when you just don’t know how loud it may get, and digital distortion can ruin an otherwise good take. Set both the COMPRESSOR THRESHOLD and RATIO relatively high, just enough to limit the peaks. Set the GATE THRESHOLD very low, though you might want to raise it just above the noise floor to get rid of tape hiss or processor noise. Of special interest are instruments which have large level differences in their tonal ranges. String pops on a bass are one example, shrill peaks on a flute are yet another. The higher tones require more breath and can seem much louder than lower pitches. Another good application would be a drum mix or vocal submix.
LONG DISTANCE LINE DRIVER
The DC22S is excellent as a line level amp for driving long lines (from the mixer to the stage for instance). With the COMPRESSOR switch in the BYPASS position, the INPUT LEVEL control and the output amplifiers remain in the circuit. This provides a very low distortion, low noise line driver. Balanced XLR connections are recommended for the long run from the DC22S's outputs (anything over 10 feet [3 meters]). A balanced piece of equipment (equalizer or amplifier) must be used at the receiving end of this long line. For unbalanced systems, use the 1/4" inputs on the DC22S and use the balanced XLR outputs to run the long distance.
SOUND SYSTEM WITH COMPRESSION
Let’s run a stereo system with compression. Patch the DC22S Compressor Inputs from the program source or mixer outputs, and send the DC22S Outputs to the system equalizer (if you have one), and then on to the crossover inputs (if you have one). Set the equalizer and crossover Inputs to unity gain. Set the LINK switch to ON, and adjust the CHANNEL 1 COMPRESSOR THRESHOLD and RATIO controls to keep the entire system dynamic range under control. Locating the compressor before the equalizer results in correct spectral balance during compression.
To individually limit Low and High drivers in a biamped system, connect the Crossover Low Output into one DC22S Input, and the High Output into the other DC22S Input. The DC22S Outputs go right to the respective low and high frequency power amplifier inputs. For a stereo configuration use two DC22S Stereo Compressors. Be sure the LINK switch is OFF. Set the RATIO controls to 10:1. Assuming your input signal has peaks in excess of -20 dBu, you should be able to rotate the COMPRESSOR THRESHOLD controls and see some GAIN REDUCTION meter action. You should begin to hear the difference. Leave these controls at whatever level is appropriate for your application. For the most precise settings, refer to the Driver Protection section in the manual.
Let’s start with what a compressor actually does. No matter how you cut it, this is an automatic volume control. It is a hand on a knob, turning the volume down and turning it up again. The hand is really quick and really accurate, but it’s just turning a volume control.
When the input signal reaches a level set by the COMPRESSOR THRESHOLD control, the compressor begins turning down the signal by an amount determined by the RATIO control. The DC22S, like most compressors, operates by making the loud signals quieter, but does not make the quiet parts louder. However, by keeping the loud signals under control, the entire system may be turned up when necessary to make the quiet parts louder.
Before proceeding, it’s a good idea to turn the control knobs to the following positions:
1. GATE THRESHOLD control fully counterclockwise
2. COMPRESSOR THRESHOLD fully clockwise
3. COMPRESSOR RATIO fully counterclockwise
4. BYPASS switches ACTIVE (out)
5. OUTPUT LEVEL 0 dB
This renders the DC22S with no compression, allowing signal through at unity gain. No change occurs with the BYPASS switch in or out.
Before making any Threshold adjustments, set the ouput level of the previous device so the +4 dBu LED lights occasionally, and the OL LED does not light. Be aware that changes to the Input Level will affect the Thresholds.
The threshold is the point at which gain adjustment begins. When the input signal is below the threshold, the DC22S attenuates the signal at a 2:1 ratio, making the quiet parts twice as quiet. When the signal is above the Gate Threshold, the Gate is open, like a straight wire. With a fixed Ratio set to 2:1, this graph shows gain reduction below various Gate Thresholds at -20 dBu, -30 dBu, -40 dBu, etc.
The threshold is the point at which gain adjustment begins. When the input signal is below the threshold, the Compressor section acts like a straight wire. When the signal is loud enough to cross the Compressor Threshold, the compressor is active and turns the volume down. Various Threshold points are illustrated below. How much it gets turned down is determined by the RATIO control ( this graph shows a Ratio set at 2:1). With the Ratio set to ∞, the DC22S acts as a Limiter. This graph shows Limiter gain reduction above various Compressor Thresholds at 10 dBu, 0 dBu, -10 dBu, etc.
Once the Threshold is exceeded, the increase in output compared to the input signal increase depends on the RATIO setting. An ordinary preamp set for unity gain or a straight wire has a ratio of 1:1, that is, the output level tracks the input level perfectly. A 2 dB change at the input produces a 2 dB change at the output. For a 10:1 Ratio, a 10 dB blast at the input would rise only 1 dB at the output -- heavy compression. Kinder, gentler ratios are in the 2:1 to 3:1 range. Limiting, with no increase in signal above the Threshold, occurs at ∞:1. The next graph illustrates various Ratios with the Threshold at -40 dBu and Ratios of 1:1, 1.2:1, 1.5:1, etc. Vertical axis = output level, horizontal axis = input level.
A limiter is a special form of compressor set up especially to reduce peaks for overload protection. In other words, it’s a compressor with a maximum ratio. A compressor is used to change the dynamics for purposes of aesthetics, intelligibility, recording or broadcast limitations. Once the threshold of a limiter is reached, no more signal increase is allowed. The DC22S acts as a limiter when set at a very high ratio of 10:1.
LINKING IN STEREO
When using the DC22S as a true stereo processor, with left signal in Channel 1 and right signal in Channel 2, it is recommended to turn the LINK switch on to prevent large balance and image shifts. While LINKed, both Channels attenuate by exactly the same amount when either Compressor works, maintaining correct stereo imaging. Only Channel 1's controls are active, Channel 2 becomes the slave.