A Dynamics processor (limiter, compressor, expander, and gate) is calculating the output gain at some point in time, and it is applying this gain at some delayed point in time.

This allows for Dynamics processor to "look ahead" and act on some audio events a few mili-seconds before they actually arrive. This is usefull in cases where sharp, transient signals occur. However, my use case is speech, in a bit noisy environment, but nothing "sharp", no transients, no drum kicks and similar.

Would adding lookahead in such a "speech" use case be beneficial?

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    $\begingroup$ It's not clear what you are asking. You can't process something before it arrives and the processing itself will require some time. A processor can "look ahead" on data that is delayed and apply itself to the delayed data. What do you mean by "actually arrive". My first Engineering class, if you didn't draw the picture the problem was marked wrong with no credit. If you drew the picture but was wrong, you got partial credit. Language is too ambiguous in many cases. Draw the picture. $\endgroup$ – user28715 Aug 24 '18 at 13:45
  • $\begingroup$ Good thing is we're not grading things, but I strongly recommend drawing pictures! Basically, whenever you feel the need to put something in quotation marks, because it's not quite the right term, then you actually need a different way of expressing it. $\endgroup$ – Marcus Müller Aug 24 '18 at 16:24

It sounds better this way.

Let's say you have limiter and you can't exceed a certain amplitude value (risk of clipping, for example). Now there is an audio event (say a snare hit) that peaks at twice that amplitude. If you just reduce this sample by sample instantaneously you create a lot of audible distortion. If you have look ahead, you can ramp down the gain smoothly so that by the time the audio even arrives, the gain is low enough so that you are not clipping any more.

Rapid gain changes tend to create a lot of audible artifacts. The look ahead buffer allows you to slow down the gain changes without the risk of creating an instantaneous out of bounds condition.

It's also useful to look at a bit in the future when determining the gain for the current sample: if that's the highest point in the waveform can slow down the gain reduction, but if it's part of a slope, you probably want to maintain or increase your gain reduction speed.

Of course, you are not actually "looking into the future". Look ahead simply means that you put a delay on the processing path but NOT on the detection path of the dynamic processor.

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  • $\begingroup$ Thanks. Adding "lookahead" in order to catch sharp transients makes sense. However, my use case is normal speech, sometimes in a bit noisy environment. Not sure if lookahead would be beneficial there too. $\endgroup$ – Danijel Aug 27 '18 at 9:43
  • $\begingroup$ I edited a question to provide more info. $\endgroup$ – Danijel Aug 27 '18 at 9:48
  • $\begingroup$ It would help what exactly you want to do and why do you think look ahead matters. There many, many different flavors of speech processing.. Depending on your application and purpose look ahead can be useful or not. $\endgroup$ – Hilmar Aug 28 '18 at 16:00

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