[op25-dev] Re: OP25 GRC - Almost but not quite working

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argilo314 argilo at gmail.com
Sun Jun 10 15:19:56 UTC 2012

I've made a bit of progress.  It appears that the phase calculation in  software_imbe_decoder::synth_voiced is not correct in the "fine transition" case, resulting in abrupt phase shifts between the 20ms frames.  I'm not sure yet how to correct it, but by commenting out the "fine transition" case completely so that the "coarse transition" case always runs instead, I've eliminated most of the warble.

Another problem I noticed is that the audio output is sometimes greater than 1.0, resulting in clipping if connected directly to an audio sink.  I corrected this by changing the "sample /= 16384.0;" line at the end of software_imbe_decoder::decode_audio back to "sample /= 32768.0;".

- Clayton

--- In op25-dev at yahoogroups.com, "argilo314" <argilo at ...> wrote:
> I'm getting the same issue with the sound: speech is intelligible but with a strong warble that makes it sound like talking through a fan.  I had a quick look at the waveform and spectrum of the output but didn't spot any obvious problems there.  Not knowing IMBE, I couldn't get far with the code.  Any ideas?
> - Clayton
> --- In op25-dev at yahoogroups.com, "rrgsti" <bobrich@> wrote:
> >
> > Basically looking at bit 113 (only) seems to indicate whether or not it's a voice frame of some sort.  The audio still sounds like everyone is talking through a fan, but there are no dropouts, no clicks, no stutters, etc.  
> > 
> > I could not find anything resembling a DUID or NAC in the headers.  If anyone has a suggestion to de-warble the audio, I would greatly appreciate it.

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