you can also run sox on a script to change the volume of the sound files by batch.
<br><br><div class="gmail_quote">On Mon, Jun 27, 2011 at 5:20 AM, Jan Berger <span dir="ltr"><<a href="mailto:jan.berger@video24.no">jan.berger@video24.no</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Wavepad is free and will do bulk changes to sound files.<br>
<br>
Won't AGC solve this?<br>
<br>
Jan<br>
<br>
-----Original Message-----<br>
From: <a href="mailto:freeswitch-users-bounces@lists.freeswitch.org">freeswitch-users-bounces@lists.freeswitch.org</a><br>
[mailto:<a href="mailto:freeswitch-users-bounces@lists.freeswitch.org">freeswitch-users-bounces@lists.freeswitch.org</a>] On Behalf Of Bryan<br>
Smart<br>
Sent: 26. juni 2011 22:32<br>
To: <a href="mailto:freeswitch-users@lists.freeswitch.org">freeswitch-users@lists.freeswitch.org</a><br>
Subject: [Freeswitch-users] Proper prompt gain/level<br>
<div><div class="h5"><br>
As part of creating prompts for my IVRs, I've tried to match the audio gain<br>
of my prompts with the gain of the stock English prompts. During this<br>
process, I noticed that the English Callie prompts are recorded extremely<br>
low (max gain around -16DB). I have the Cepstral Callie voice, and I must<br>
set the Cepstral volume to about 50% in order to match the gain of the<br>
English prompts. In conferences and other situations where prompts are<br>
played over conversations, the level of the prompts are obviously low.<br>
<br>
I can, of course, renormalize the gain of the prompts up to -10DB or more<br>
with a sound editor. However, I wonder if there is a better way to change<br>
the level of the prompts, or if there is a good reason for the prompts to be<br>
encoded at such a low level.<br>
<br>
I haven't considered all of the implications yet, but I'm fairly sure that<br>
encoding the prompts this quietly is not the best approach, even if it is<br>
desirable for the prompts to play quietly on a call. For each 6DB reduction<br>
in gain, there is a 50% reduction in perceived volume, and one less<br>
significant bit is used for storing the audio. In a 16-bit file, a maximum<br>
gain of -16 means that only the 14 least significant bits are actually used<br>
for encoding the audio. This results in a reduction in dynamic range, but<br>
the difference isn't really noticeable as long as the data remains 16-bit.<br>
The problem comes when the audio is converted to a different bit depth. For<br>
example, most quickie routines for converting 16-bit audio to 8-bit audio<br>
will simply chop off the 8 least significant bits. Therefore, when the<br>
prompts are converted to 8-bit audio for use by most of the narrow band<br>
codecs, the prompts are only using 6 bits of audio. If the volume of the<br>
channel is increased, then the<br>
6 bits are promoted, and the dithering errors at the bottom become louder.<br>
In the worst case, since these prompts are only encoded with 14 bits of<br>
actual data, and converting to an 8-bit channel will only leave 6 bits of<br>
actual data, boosting the gain of the prompts on an 8-bit channel to full<br>
loudness would result in the noise floor (the level of the dithering<br>
crackle) being about -18DB. That's almost as loud as the prompts themselves<br>
sound at the moment.<br>
<br>
Anyway, regardless of observations, is there a reason why the prompts must<br>
be recorded so quietly? If I'd like them louder (without increasing the gain<br>
of the entire channel), is there a way other than running them through a<br>
tool to renormalize their max levels?<br>
<br>
Bryan<br>
<br>
<br>
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</div></div></blockquote></div><br>