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Chapter 5

30 ALESIS ML-9600 REFERENCE MANUAL

5.4C DSP3:LOOK-AHEAD PEAK LIMITER

The Look-Ahead Peak Limiter is designed to give you the ability to limit the highest peaks in a Track

and simultaneously bring up the gain of the Track in order to maximize its level before creating a CD.

This allows you to "squeeze" that extra couple of decibels out of the dynamic range, without squashing

your audio by hard compression or traditional limiting.

The limiter in the ML-9600 is very different than a traditional limiter, which is typically thought of as a

compressor with a high ratio setting. By virtue of all-digital processing, the limiter is able to "look

ahead" in time to see audio level peaks. This allows the limiter to begin smoothly reducing the gain of

the audio so that when the peak does occur, it is limited to the desired value. In essence, the limiter

becomes a "perfect" limiter or one capable of attaining an infinity-to-one gain reduction ratio.

Another difference from a traditional limiter is that the "make-up" gain is automatically applied as a

function of the threshold level. This allows the limiter to act as a "maximizer", enabling you to bring

your Tracks very close to the maximum level allowed without clipping.

The final difference in this limiter is that the final output level can be fixed as a function of full-scale; i.e.

the limiter has infinity-to-one compression ratio with an extra gain stage at its output. This allows you

to decide what the peak output value of the audio will be (-0.2dBFS, for instance).

The Look-ahead peak limiter is perhaps best thought of as three discrete gain blocks:

• The first gain block is dynamically adjusted so that its output level never exceeds the threshold

level (the "perfect" limiter).

• The second gain block adds make-up gain to the signal equal and opposite to the threshold value (a

threshold value of –10dBFS would have 10dB of make-up gain applied).

• The third gain block is a "scaling" gain block; it allows you to select the exact maximum output

level (as a function of full-scale). If this gain block were not there, the automatic make-up gain

would cause all signals that reached the threshold to equal 0dBFS.

There are only three parameters in the limiter DSP block, so it is extremely easy to set up and use. A

detailed look at each of the parameters follows.

Threshold

The Threshold parameter of the limiter sets the maximum output level from the first gain stage. No

gain reduction is applied as the signal level approaches the threshold, but once it does, the limiter holds

the output of that stage to the threshold value. Make-up gain is applied to the audio after it has been

limited to the threshold value, so if audio is playing while the threshold parameter is adjusted

downward, the output audio will appear to get louder. The threshold parameter is adjustable from –

0dBFS to –65dBFS in 0.5dB increments.

Output Level

The Output Level parameter sets the absolute maximum output level from the limiter, as a function of

full-scale. A value of –0.1dB will limit the output audio to no greater than –0.1dBFS, regardless of input

level or threshold setting. The output level parameter is adjustable from 0dBFS to –65dBFS in 0.1dB

increments.

Release

The release parameter functions exactly like its counterpart in the compressor; it controls how long gain

reduction is applied to the audio after the input signal drops below the threshold. Release is adjustable

from 0 microseconds to 9.9 seconds.

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Alesis MASTERLINK ML-9600 Informations techniques Page 40

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