ALESIS 3630 Reference Manual
1.1 INTRODUCTION Thank you for purchasing the Alesis 3630 Dual Channel Compressor/ Limiter with Gate. This cost-effective gain control device complements any studio with several important features. For more information on the significance of these features, refer to the Appendix "About Compression and Limiting." • Stereo or dual mono operation. The 3630 can serve as two totally independent units, or both sections can be strapped together for stereo operation.
Here are some typical applications for the 3630: • Even out a vocalist's dynamics to compensate for poor mic or vocal technique. • Increase a guitar's (or other stringed instrument's) sustain. • Smooth out bass sounds for a more consistent level. • Prevent peaks common in many source signals, such as drums, from overloading tape during recording. • Minimize the chance of speaker burnout by inserting a limiter prior to the power amp.
nels, synthesizers, and other unbalanced signal sources. Microphones and guitars can be used with the level switch set to -10dBV (see below). Guitars with exceptionally low output pickups may require a preamp for best results. The input impedance is greater than 100kΩ. Side chain This stereo jack allows for insertion of other signal processors or "keying" from other signal sources. See section 1.8 for side chain applications. Output Provides the processed (compressed/limited/gated) output.
1.3 HOOKING UP POWER Hooking up power involves the rear panel power jack and front panel on-off switch. Power jack Plug the AC adapter output in here. Use only the AC adapter supplied with the 3630; use of any other AC adapter will void your warranty. To prolong the AC adapter's life, unplug it when not in use (turning the 3630's power switch to off is not sufficient to disconnect the AC adapter from AC power).
Threshold (-40 to +20 dBu) Sets the level above which signals will be compressed or limited. Rotating the control clockwise raises the threshold, thus clamping signals at a higher level and reducing the amount of compression or limiting. Ratio (1:1 to ∞:1) Sets the compression slope, which determines how the output signal will change in relation to the input signal once the input signal exceeds the threshold. The first digit indicates how many dB of input change will cause a 1 dB output change.
Peak mode. RMS mode automatically adjusts the attack time, depending on the characteristics of the signals being processed. In p e a k m o d e , this control sets how fast the limiter's internal circuitry reacts to changes in input level. The longer the attack time, the more of a signal's dynamics are "let through" before the limiting action kicks in. With slower attack times, the limiter responds more to average signal level.
1.5 FRONT PANEL COMPRESSOR/LIMITER SWITCHES Each switch has an in and out position. The legend above each switch shows which status is associated with which switch position. Peak - RMS With peak response, the 3630 responds to signal peaks to insure that these peaks do not exceed a particular threshold. This mode is ideal when using the 3630 to avoid clipping, a phenomenon when signal peaks exceed a particular device's headroom. In RMS mode, the 3630 responds to a signal's average level.
goes into limiting. With the Link switch out, Channels A and B operate independently as two monophonic compressor/limiters. With the Link switch in, Channel A's controls become master controls for Channels A and B, with the exception of the input/output and the +4 dBu/-10 dBV switches which will continue to operate independently. The stereo signal is processed identically by both channels to preserve proper stereo imaging.
Threshold to OFF. Turn on all instruments to be gated but do not pass program material through them (For example, turn your microphone on but do not sing through it). Increase the Threshold (clockwise) until the red CLOSE LED comes on. Any background noise should now be eliminated. Example: To remove hiss from a guitar amp signal, set the Threshold just above the residual hiss while muting the guitar strings. Playing guitar should produce a signal higher than the threshold, letting through the notes.
Noise Gate Meter (Open or Closed) When the noise gate is closed (i.e., the input signal is below the noise gate threshold), the red Close LED is lit. When the noise gate is open and letting through the input (i.e., the input signal is above the noise gate threshold), the green Open LED is lit. The red Close LED fades from on to off over the time set by the noise gate Rate control. Since either the Open or Close LED will be on at all times, these also serve as power-on indicators. 1.
Keying Application: Ducking A typical use of keying is to lower background music in the presence of narration. This is called ducking because the music "ducks" to get out of the way of the narration. A similar application would be to lower the level of a rhythm guitar while a vocalist is singing. To perform ducking: 1. Process the signal to be "ducked" (e.g., background music) through the 3630. For stereo signals use both channels, for mono signals just use one channel. 2. Plug the control signal (e.g.
Frequency-Dependent Limiting Application: De-Essing Some vocalists and announcers, especially if equalized for more treble, will produce excessive "sibilance" ("S" sounds, concentrated mostly in the upper midrange and treble). In this situation, the limiter would ideally limit the signal only when high frequency "S" sounds occur. This is possible by inserting an equalizer into the side chain jack.
1.9 TROUBLESHOOTING Noisy or "squeezed" sound- Too low a limiting threshold and/or too high a compression ratio can result in such problems as squeezed, unnatural sounds or excessive noise. Remember, limiting lowers the input signal's dynamic range. If the input signal has a dynamic range of 60 dB and you apply 15 dB of limiting (quite a lot), the dynamic range falls to 45 dB. This degrades the signal-to-noise ratio by an equal amount.
Heavy distortion- If the +4/-10 switch is set to -10, try setting it to +4. Gate opens but will not close again- This may be caused by improper Threshold adjustment. Reset the gate as explained in Section 1.6, under Threshold. Gate "chatters"- Reduce Threshold level and/or increase Rate control until a smooth transition occurs. 1.10 3630 SPECIFICATIONS Dynamic Range: >118dB, "A" weighted Signal to Noise Ratio: >100dB, "A" weighted Headroom: +18dBu Frequency Response: 10Hz to 30kHz, 0/-.
1.11 APPENDIX: About Compression, Limiting, and Noise Gating Compression and limiting both affect a signal's dynamic range, although in slightly different ways. This type of signal processing can be used as an effect (e.g., increase a guitar or cymbal's sustain) or for more practical applications, such as avoiding tape saturation or restricting the dynamic range of program material for broadcast applications.
AMPLITUDE VS. TIME However, the maximum peak signal level has gone from 100 in the first drawing to 50 in the second drawing. Therefore, the overall signal sounds softer. By adding output gain, we can give the limited signal a peak value of 100 again. AMPLITUDE VS.
This limited, amplified signal has a much higher average level than the original signal. This is why limited signals can "jump out" at you and have more punch. Commercials, for example, are often heavily limited so that they have as high an average signal level as possible. Radio and TV stations also use limiting to cope with the medium's limited dynamic range.
The speed with which a limiter responds to the input signal is also important. If the limiter tries to follow every little nuance of music, the sound can be overly "choppy." Often, you'll want the limiter to affect dynamic range over a somewhat longer period of time. The Release control sets this time period. Clamping a signal too rapidly can greatly reduce a transient, producing a somewhat dull sound. The Attack control determines how long it takes for the limiter's clamping action to begin.
Noise Gating To understand a gate's principle of operation, consider a "manual noise gate." Suppose you're listening to an audio signal being processed by a relatively noisy effect. As long as the audio signal is present, its level will generally be higher than the noise, thus masking it. However, when the audio signal goes away, the noise is no longer masked and can be heard.
