Author Topic: CDP programs not doing floating point processing right?  (Read 719 times)

Xenakios

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CDP programs not doing floating point processing right?
« on: June 27, 2014, 11:31:27 AM »
I now (re)discovered that prepending "-f" to the output file name of the (time domain(*)) programs, a 32 bit floating point file will be produced. However, it looks to me that the processing internally is not floating point or is handled incorrectly.

A simple test : use the modify loudness program to increase the volume of an already loud 16 bit file that has peaks at the maximum range, using the -f option. The expected result is that when the resulting file's volume is again reduced enough in some program known to do the floating point calculations as expected (such as Cockos's Reaper), there would be no distortion. The files obtained from the CDP modify loudness program however do not behave like that. They are permanently clipped to produce distortion. This leads to me to believe that either the internal processing does not happen as floating point or that the output is clipped into the -1.0...1.0 range, effectively making the floating point output file option nearly useless. The same behavior can be observed with the other CDP programs, but modify loudness is the clearest way to reproduce this behavior.

I don't bring this up due to "golden ears" concerns. The value of having a clean 32/64 bit floating point processing chain to me is almost entirely in the available volume headroom when the processing chain is working correctly. Ie, even if a DSP calculation ends up producing samples beyond the nominal -1.0...1.0 range, the signal can later be brought down in volume to not distort the monitoring output or to make it work better when mixing. If how this is supposed to work is not clear from the description, I can produce a demonstration as a video or a set of audio files.

(*) It seems that the spectral processings now always result in 16 bit PCM files, which seems like an obvious bug. (Unless the pvoc program and the CDP programs that transform the .ana files actually just are 16 bit only...?)

rwdobson

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Re: CDP programs not doing floating point processing right?
« Reply #1 on: June 27, 2014, 12:48:14 PM »
This is (another?) case of an under-documented feature. CDP looks for a environment variable CDP_NOCLIP_FLOATS, and writes unclipped floating-point files if it is found. The unattractive alternative would be to add such a flag to each and every command line program in the system.

On the Mac you can just use the "export" command in Terminal at the start of a console session:

export CDP_NOCLIP_FLOATS=1

Or on Windows use "set" in the same way. If you want this established permanently you can use the OS facilities to define CDP_NOCLIP_FLOATS at startup, as for any other environment variable.

The usefulness of this depends somewhat on using the full CDP soundfile header (as used by default) which supports the PEAK chunk. The CDP play programs (paplay, pvplay) will read this if found (as does for example the program "sfprops" from the toolkit) , and automatically scale down any overrange f/p soundfiles so they will render cleanly. This may lull you into a false sense of security though!



Xenakios

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Re: CDP programs not doing floating point processing right?
« Reply #2 on: June 27, 2014, 05:39:24 PM »
This is (another?) case of an under-documented feature. CDP looks for a environment variable CDP_NOCLIP_FLOATS, and writes unclipped floating-point files if it is found.

Oh, very interesting, thanks! I will test ASAP!

Xenakios

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Re: CDP programs not doing floating point processing right?
« Reply #3 on: June 27, 2014, 05:47:00 PM »
Excellent, the CDP_NOCLIP_FLOATS environment variable appears to work! ;D

usw

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Re: CDP programs not doing floating point processing right?
« Reply #4 on: July 25, 2014, 07:50:41 PM »
I'm so glad I signed in, thank you both, for the question and the fortunate workaround  ;D