the limiter in scriptfx can't brickwall

[NEST.acoustics]

Even when I extend the ratio to 100, the attack still lets overs through - but turning the attack to 0 makes it super clicky. Is there a simple brickwall limiter trick anyone knows in scriptfx?

[ustk]

@NEST-acoustics Without a lookahead capability, my guess is that any simple limiter set with a 0ms attack will be nothing but just a clipper...
I am not aware of a ready made solution, so you might end up to make your own DSP research for such extreme settings.

[Dan Korneff]

There are some helpful notes in the source code:

        /* REGARDING THE MAX PEAK: This method assumes that the only important
         * sample in a look-ahead buffer would be the highest peak. As such,
         * instead of storing all samples in a look-ahead buffer, it only stores
         * the max peak, and compares all incoming samples to that one.
         * The max peak has a hold time equal to what the look-ahead buffer
         * would have been, which is tracked by a timer (counter). When this
         * timer expires, the sample would have exited from the buffer. Therefore,
         * a new sample must be assigned to the max peak. We assume that the next
         * highest sample in our theoretical buffer is the current input sample.
         * In reality, we know this is probably NOT the case, and that there has
         * been another sample, slightly lower than the one before it, that has
         * passed the input. If we do not account for this possibility, our gain
         * reduction could be insufficient, resulting in an "over" at the output.
         * To remedy this, we simply apply a suitably long release stage in the
         * envelope follower.
         */


        /* REGARDING THE ATTACK: This limiter achieves "look-ahead" detection
         * by allowing the envelope follower to attack the max peak, which is
         * held for the duration of the attack phase -- unless a new, higher
         * peak is detected. The output signal is buffered so that the gain
         * reduction is applied in advance of the "offending" sample.
         */

         /* NOTE: a DC offset is not necessary for the envelope follower,
          * as neither the max peak nor envelope should fall below the
          * threshold (which is assumed to be around 1.0 linear).
          */


        /* REGARDING THE GAIN REDUCTION: Due to the logarithmic nature
         * of the attack phase, the sidechain will never achieve "full"
         * attack. (Actually, it is only guaranteed to achieve 99% of
         * the input value over the given time constant.) As such, the
         * limiter cannot achieve "brick-wall" limiting. There are 2
         * workarounds:
         *
         * 1) Set the threshold slightly lower than the desired threshold.
         *        i.e. 0.0dB -> -0.1dB or even -0.5dB
         *
         * 2) Clip the output at the threshold, as such:
         *
         *        if ( in1 > thresh_ )        in1 = thresh_;
         *        else if ( in1 < -thresh_ )    in1 = -thresh_;
         *
         *        if ( in2 > thresh_ )        in2 = thresh_;
         *        else if ( in2 < -thresh_ )    in2 = -thresh_;
         *
         *        (... or replace with your favorite branchless clipper ...)
         */
    }