Alesis 3630 Compressor Dynamics Processor
A great choice for recording, mixdown, instrument rigs, and sound reinforcement, the Alesis 3630 Compressor provides two independent full-featured compressor/ limiters in one rack space while offering excellent sonic quality for any application from studio recording to live sound or broadcast. As an independent dual-channel compressor, the 3630 offers separate controls for two different source signals. Plus, two fully independent gates with threshold and rate controls allow you to easily and efficiently stifle unwanted ambient noise.The Alesis 3630 Compressor (seelarger image).The 3630 offers Ratio, Threshold, Attack and Decay controls to customize its compression response for even the toughest signals. You can also choose between RMS and Peak compression styles, plus Hard and Soft Knee dynamic curves for every application from subtle gain control to in-your-face punch. Other advanced dynamics processing features include precise signal metering, a sidechain for keying or ducking effects, and stereo linkable operation.SpecificationsThreshold (dB):-40 to +20 dBRatio:1:1 to inf:1Attack Times:0.1 to 200 ms/prog dependentRelease Times:50 ms to 3 secondsGain Control:OutputBypass Switch:YesNumber of Channels/Stereo Link:2/YesMeter Type (VU, LED, etc.):12-segment LEDMain I/O Types (XLR, 1/4-inch, etc.):1/4-inchSidechain I/O Types (XLR, 1/4-inch, etc.):1/4-inch TRSDimensions:19 x 1.7 x 4.5 inches (WxHxD)The Channel A controls.The Channel B controls.About Compression, Limiting, and Noise GatingCompression 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.LimitingA limiter does not affect the signal going through it until that signal reaches a particular threshold. Above this threshold point, the limiter prevents the signal from becoming any louder by providing as much attenuation as is needed to keep the signal from exceeding the threshold. If the signal drops below the threshold, then the limiter "goes back to sleep" and leaves the signal alone unless it exceeds the threshold again.Hard knee response (above) and soft knee response (below).If the limiter's clamping action occurs abruptly--in other words, the limiter goes from no limiting to full limiting at the threshold point--the sound's output level will not increase despite changes in input level. This is called ahard kneeresponse and is often used to eliminate loudspeaker or amplifier clipping. With asoft kneeresponse, the limiting action becomes progressively greater past a certain point until it eventually flattens out and clamps the signal fully, just like a hard-knee limiter. This tends to produce a smoother limiting sound that helps smooth out an instrument's 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.CompressionCompression is similar to limiting, but rather than clamp all signals to a constant threshold, the output changes at a lesser rate than the input. For example, with a 4:1 compression ratio (as set with the ratio control), a 4 dB input level change produces a 1 dB output level change; an 8 dB input level change produces a 2 dB output level change.Noise GatingTo 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.If you connected a volume control after the noisy effect, you could eliminate the noise by turning down the volume whenever there was no audio signal. Then, as soon as the audio signal (which masks noise) returned, you could turn the volume up again.A noise gate performs a similar function, but automatically. You set a particular noise gate threshold, and the gate compares the input signal level to that threshold. If the input signal exceeds the threshold, the gate acts like a volume control that's all the way up, and lets the signal through. If the input signal is lower than the threshold, the gate acts like a volume control that's all the way down, and blocks the input from reaching the output. If the threshold is set just above the residual noise level, then the gate will be closed whenever there is hiss, thus giving a quieter signal.