[Asterisk-Users] Re: wav instead of gsm for vm-sounds?

[Tony Mountifield]

Damon Estep <damon at suburbanbroadband.net> wrote:
> Tony Mountifield wrote:
> > Do wav or sln versions exist of the standard Asterisk sounds by
> > Allison?
> > I mean the versions before GSM compression was applied, not just ones
> > obtained by uncompressing the GSM again.
> 
> Not sure about that Tony, we recorded a full set of sounds on our own so
> we would have a consistent voice in our customizations. We also change
> all of the references from 'extension' to 'phone number'
> 
> It took a little time, but well worth it.

Damon, thanks for the tips on recording (below). I was particularly
interested in the 10% time reduction. I had a few questions about
it:

a) are you doing a straight "speed-up", so that the frequency increases
by 11% as well as the speed? Or are you doing a pitch-preserving duration
adjustment?

b) You mentioned using 32kHz sampling to avoid artefacts, but doesn't
the time reduction conflict with this?

c) What is the nature of the perceived improvement? Does it make the
announcements just sound snappier?

Cheers
Tony

> We used a creative labs audigy sound card(good SNR) on a windows machine
> with a good mic and then processed the sounds in adobe audition,
> applying a high pass filter, low pass filter, silence removal, sound
> level normalization, and a 10% time reduction. The 10% time reduction
> and silence removal really helps things sound professional.
> 
> We started with 16bit, 32khz, mono pcm wave files, we then did our
> processing, saving the file as 16bit, 8khz, mono after the processing
> and then finally converting to ulaw files using sox and a script found
> on the wiki with a few changes.
> 
> 32khz gives good resolution for processing, and scales to 8khz well as
> it is a multiple of 8khz. 44khz is trickier to scale to 8khz and may
> result in some artifacting. 8khz is not a high enough sample rate to get
> good filter processing with some of the adobe filters.
> 
> Here is the script I used in sox to do the final conversion;
> 
> # for a in *.wav; do sox $a `echo $a|sed -e s/wav//`ul ; done
> 
> Thanks to Kevin flemming for pointing me in the right direction on this.
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org