On Tue, 2004-04-13 at 01:12, James Gardiner wrote: > Hi all, > I am not sure if tis is a bug but.. > Was learning about VM etc to see how it all worked, and I noticed the > following.. > > In the default install, the VM system leaves 3 different copies of the Voice > message. > Size filename > 13kb Msg0000.gsm
This is a raw gsm frame dump of the audio. It contains no headers for a sound editing app to understand it. > 13kb Msg0000.wav This is the previous GSM frames wrapped in a RIFF wav header and the appropriate bit shifting to make windows happy. > 122kb Msg0000.WAV <- under UNIX we have case sensitive file names of > course. This is raw PCM. That is why it is larger. > I wanted to have a look at these files so loaded them into SOUND FORGE 6. > This first thing I noticed was that the LARGER file is of much HIGHER > volume. Like it had been normalised to 100% > The smaller was file, when loaded into sound forge, did not load properly, > only the first 2 seconds loads. > > Can anyone explain these issues and why they exist? For some reason the PCM files are bit shifted up. This gives the effect of doubling the volume. If I understand it though, it is also bit shifted down when played back via asterisk. So you loose the volume if asterisk replays the audio file. > All in all, I was wondering what would be the best format for best quality > but with still great compression. GSM is fine enough for the prompts. > I want to archive all calls for a period of time with self expire. (For > example dedicate 5 gig disk space to the last number of calls that can fit > in the 5gig.) I want to store the best quality possible but also make best > use of disk space, so I can store for even longer periods. I was > considering ogg but then is occurred to me that GSM or other codecs designed > for audio with this frequency response may be better. (But the GSM file > above is not as clear as the WAV ones produced.) GSM is good. 33 bytes per 20ms will get you a long ways. From what I see, here is your capacity. (5*1024*1024*1024)/(50 blocks a second * 33 bytes per block)/60 seconds per minutes /60 minutes per hour and you get 903 hours. then remove a certain amount for disk block alignment, formatting, and the lost fragments at the end of a 4k cluster and you are now down to a realistic 800 hours of record time or 33 and a 3rd hours of a constant T1 of audio calls. > I was also wondering if the VM system when emailing the audio can be setup > to use something like ogg or MP3? ogg and mp3 are not good choices for telephone quality. They don't get that great of compression unless you start sacrificing a lot of quality. -- Steven Critchfield <[EMAIL PROTECTED]> _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
