Re: Audio Compressor

Hi,

Em ter., 18 de ago. de 2020 às 16:27, Ian McCallion <[email protected]>
escreveu:

> 1. Your while loop looks very strange to me and I believe the identical
> result would be achieved much faster by simply omitting the while and
> endwhile statements.
>

Without the "while" will not be possible get the Crest Factor desired,
because when I just set everything greater than 1 to 1, and everything
lower than -1 to -1, the RMS level will be changed.
The "while" function will check the newer RMS level and calculated it again.


> 2.  The statement:
>      normalized = filtered / (rms(filtered) / 10^(-crest_factor/20));
>      normalises the signal to an RMS level of -6dB below 1. An RMS below 1
> does not of
>      course guarantee there will be no samples greater than 1, but unless
> your signal is very
>      peculiar I would expect there to be very few or none.
>

This is why I'm using the "while" function, to reduce the number of samples
greater than 1 & lower than -1


> Possibly therefore the following code would meet your needs without the
> need for complex compression.
>
> crest_factor = 6;
> typenoise = noise(10*44100, 1, 'pink');
> [z, p, k] = butter(4, [100/(44100/2), 500/(44100/2)]);
> sos = zp2sos (z, p, k);
> filtered = sosfilt(sos, typenoise);
> normalized = filtered / (rms(filtered) / 10^(-crest_factor/20));
> NumberOfClippedSamples = nnz( normalized > 1 |normalized<-1)
> normalized(normalized > 1) = 1;
> normalized(normalized < -1) = -1;
>

In your example, I'm getting a Crest Factor of -6,36 instead of -6 (this
0,36dB is too much) and almost 20000 samples clipped.
I would like to avoid this approach "*normalized(normalized > 1) = 1*" to
avoid a* hard clipping*.
What I'm looking for is a kind of Hard Limiter instead of a Hard Clipping.

Many thanks,
Renato