[Csnd] Multiband Compressor Program
| Date | 2017-12-04 23:31 |
| From | Emmett Palaima |
| Subject | [Csnd] Multiband Compressor Program |
Hi, I am looking into designing a multi-band compressor program and was wondering if anyone could provide advice on how such programs go about dividing and processing the different frequency bands.
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The way I first thought of was simply using butterworth filters to separate the input into several parallel compressors then summing the output, but this type of filtering seems as though it would leave audio artifacts on the output even at low compression settings. The other way I could think off would be separate the bands using butterworth filters, compress the bands, then calculate the difference in amplitude between the compressed and uncompressed bands. This could then be subtracted from the input to produce phase cancellation. This second method is a little more complicated, but it has the advantage of leaving the input audio mostly unaffected at low compression values. I am wondering if this is a common technique. I am just beginning to explore this effect so any advice on the subject is greatly appreciated. Let me know. Thanks! |
| Date | 2017-12-04 23:47 |
| From | "Jeanette C." |
| Subject | Re: [Csnd] Multiband Compressor Program |
Dec 5 2017, Emmett Palaima has written:
> Hi, I am looking into designing a multi-band compressor program and was
> wondering if anyone could provide advice on how such programs go about
> dividing and processing the different frequency bands.
Hi Emmett,
a very rough introduction, as it was given to me, some years ago. For
finer details, let's hope for the gurus. :)
You take band pass filters or combined low and high pass filters. The
difficulty is, to calculate the cutoff frequencies, so that the
frequency spectrum stays unaffected with no further processing. I.e. you
have to consider the filter slopes and how far you have to separate the
cutoff frequencies, so that they overlap with almost no drop in volume.
But I didn't understand the calculation formula at the time and it's so
long ago that it would take ages to find the exchange in my local
archive.
Another important factor is to have the same lookahead time for all
compressors or adjust the delay for longer lookahead times, othersie you
get anything from a comb filtering effect to audible delays between your
bands.
And the rest is informed expert's knowledge. Hope that's a good starting
point for the moment.
Best wishes,
Jeanette
...
--------
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| Date | 2017-12-05 08:00 |
| From | Anders Genell |
| Subject | Re: [Csnd] Multiband Compressor Program |
One way might be to use ISO standardized 1/3-Octave band filters. One implementation for Matlab/GNU-Octave by Christophe COUVREUR that I’ve used often is included below. Maybe it could be implemented in Csound? It can be found at https://se.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A1034 function [B,A] = oct3dsgn(Fc,Fs,N); % OCT3DSGN Design of a one-third-octave filter. % [B,A] = OCT3DSGN(Fc,Fs,N) designs a digital 1/3-octave filter with % center frequency Fc for sampling frequency Fs. % The filter is designed according to the Order-N specification % of the ANSI S1.1-1986 standard. Default value for N is 3. % Warning: for meaningful design results, center frequency used % should preferably be in range Fs/200 < Fc < Fs/5. % Usage of the filter: Y = FILTER(B,A,X). % % Requires the Signal Processing Toolbox. % % See also OCT3SPEC, OCTDSGN, OCTSPEC. % Author: Christophe Couvreur, Faculte Polytechnique de Mons (Belgium) % couvreur@thor.fpms.ac.be % Last modification: Aug. 25, 1997, 2:00pm. % References: % [1] ANSI S1.1-1986 (ASA 65-1986): Specifications for % Octave-Band and Fractional-Octave-Band Analog and % Digital Filters, 1993. if (nargin > 3) | (nargin < 2) error('Invalide number of arguments.'); end if (nargin == 2) N = 3; end if (Fc > 0.88*(Fs/2)) error('Design not possible. Check frequencies.'); end % Design Butterworth 2Nth-order one-third-octave filter % Note: BUTTER is based on a bilinear transformation, as suggested in [1]. pi = 3.14159265358979; f1 = Fc/(2^(1/6)); f2 = Fc*(2^(1/6)); Qr = Fc/(f2-f1); Qd = (pi/2/N)/(sin(pi/2/N))*Qr; alpha = (1 + sqrt(1+4*Qd^2))/2/Qd; W1 = Fc/(Fs/2)/alpha; W2 = Fc/(Fs/2)*alpha; [B,A] = butter(N,[W1,W2]); Regards, Anders
|
| Date | 2017-12-05 08:20 |
| From | Victor Lazzarini |
| Subject | Re: [Csnd] Multiband Compressor Program |
|
there are a number of eq filters in Csound. eqfil is one of them. Just connect them in series, and space the filter as you like. Victor Lazzarini
Dean of Arts, Celtic Studies, and Philosophy
Maynooth University
Ireland
|