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Your Thoughts on Look-Ahead Peak Limiting and Mastering, Threshold settings, etc

Well, I just received my Alesis Masterlink ML-9600 and I absolutely love
this unit. It is a dream come true for live recording and
archiving...especially so because I can burn CDs of my performance right
there on stage from the unit's hard drive. The recording quality is
immaculate and I really like the DSP, non-destructive editing features.

Anyway, I'd like some feedback from some of the other sound engineers
out there. I understand compression and limiting reasonably well (the
mathematics of compression, ratios, etc) and use it frequently in both
live and recording/sound engineering contexts.  However, this Mastelink
has a "look-ahead peak limiting" function, which as the manual says, 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."  After messing around with this, I am
very pleased with the results, but I'd like some thoughts what others
are using for output and threshold levels.  First of all, I'm targeting
-3db or -4db as my max. output level, which is pretty much industry
standard these days for CDs, 16 bit, and 44.1K.   Right now, I have the
output of the look-ahead peak limiter set to -4db and my threshold is
set to -3db. This seems to work well.  Based on some guidelines I've
seen for limiters, threshold is typically set at the max. desired
output, and output perhaps just a sliver below this max. output, which
is what I've done here. I could have set both the same as well.

What are some of you, who do your own mastering, using for limiting
setting guidelines? Better yet, if you are using a look-ahead limiter,
what setting guidelines or rules of thumb are you using for that?   For
you techies, I've copied the manual description of this function below,
so you can how it works differently than a traditional limiter or
compressor. It's almost like a limiter, expander, and compressor all
wrapped up into one function.

I can't seem to fine any good guidelines on the web either, regarding
look ahead  peak limiting. This functions seems quite a bit more
sophisticated than standard compression or limiting.

Krispen Hartung 
View improvisational / real-time looping videos:
Interactive tour of my gear: http://www.boisemusicians.com/gear.htm


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

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.


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.


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.