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

[Damon Estep]

> 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
> 

The filter we use compresses the length without changing the pitch; I
tried that with a few freeware programs, but did not get the results I
wanted until using audition. The nice part about audition is if you can
get what you need done in 30 days there is a trial! We ended up buying
it since it worked well and we host a fair number of IVRs that are
always changing.

I really have no idea how the time compression works, but the sample
rate before and after the compression is still 32khz, so the conversion
to 8khz is cleaner (every 4th sample).

I listened to a lot of IVRs over the years, including many recorded by
the well known "worldly voices" commercial robbery service.

The traits of a good recording are always the same, good dynamic range,
but even average sound level (normalization), consistent space between
words (silence removal with a consistent threshold), no mic pops (10th
order high pass filter at 150hz), and no hiss (1st or 2nd order filter
at 2khz), and finally, good pronunciation, which is easier to do talking
slower, then fix it with software magic to make it sound like your voice
model is a fast talker that never has to breath...

I do not want to take anything away from the default sounds in asterisk;
Alison has a good voice for it. Our primary goal was voice consistency
with our entire system and a "makeover" to change "extensions" to "phone
number" to better suit our application.

Of course once you do the work, you have a lot of flexibility with
format since you are down sampling, not up sampling. That is where I
needed the help.

I though I would expand on this thread a little since I did spend a fair
amount of time on the wiki pages only to learn that there is little
related information, and what is there is inaccurate or incomplete.
Nowhere on the wiki will you find a recommendation like the one Kevin
gave to use the native codec format for all sounds. In fact all
references assume .wav or .gsm files. The reality is you want to have a
format that matches each codec you use.

Damon