Microsoft WAV vs. Generic WAV "Speech Lover" <vince_zwp[ at ]hotmail.com> 5/1/2007 11:11:40 PM First of all thanks for your sincere help. I have a question regarding WAV->MP3 encoding. My IVR application records WAV files in a SALT-format of mu-law 8KHz 8kbps mono, and I need to programmatically convert them to MP3 format for another application. I searched the Internet for a SDK and found a couple of them that might do the work. One is Audio Developer SDK and the other one is Audio Format SDK. Here's the problem: When I convert a general WAV file (WAV PCM signed 16bit 16KHz 256kbps mono) to MP3, no problem! When I convert a WAV file generated from Microsoft SASDK, it fails. It appears they complain the same thing - 8KHz sample rate is NOT supported. My stupid question is: what makes the difference between Microsoft WAV format and a generic WAV format? Is Microsoft WAV format called ACM WAV? Could you recommend any MP3 encoder? Thanks again for your help Vince

Re: Microsoft WAV vs. Generic WAV "Chris P." <msdn[ at ]chrisnet.net> 5/2/2007 3:11:25 AM On Tue, 1 May 2007 16:11:40 -0700, Speech Lover wrote: [Quoted Text] > My IVR application records WAV files in a SALT-format of mu-law 8KHz 8kbps > mono, and I need to programmatically convert them to MP3 format for another > application. I searched the Internet for a SDK and found a couple of them > that might do the work. One is Audio Developer SDK and the other one is > Audio Format SDK. > > Here's the problem: > When I convert a general WAV file (WAV PCM signed 16bit 16KHz 256kbps mono) > to MP3, no problem! When I convert a WAV file generated from Microsoft > SASDK, it fails. It appears they complain the same thing - 8KHz sample rate > is NOT supported. > > My stupid question is: what makes the difference between Microsoft WAV > format and a generic WAV format? Is Microsoft WAV format called ACM WAV? > Could you recommend any MP3 encoder? There only is one WAV format, that is the RIFF/WAVE type. However there are many different types of data that can be placed inside the container, such as your mu-law data. There are various conversion techniques such as ACM, but they only allow one step conversion. E.g. to convert from mu-law to mp3 you first have to convert the mu-law to PCM and then to mp3. Depending on what mp3 encoder you have installed it might not work at 8kHz either. In general mp3 is a very poor choice for this type of data, it does not do well at low bitrates. If your target bitrate is 32kbit ADPCM is a good choice, below that the speech codecs do best, e.g. Speex, G.729. -- http://www.chrisnet.net/code.htm [MS MVP for DirectShow / MediaFoundation]

Re: Microsoft WAV vs. Generic WAV "Speech Lover" <vince_zwp[ at ]hotmail.com> 5/2/2007 4:11:00 PM Thanks again for your help Chris. I am able to save files in either PCM format or u-LAW format. Can you tell me where I can download ACM library for conversion of PCM to MP3 so I can give it a try? thanks, Speech Lover "Chris P." <msdn[ at ]chrisnet.net> wrote in message news:naauc8cgsewf.192lq7ukt1wof.dlg[ at ]40tude.net... [Quoted Text] > On Tue, 1 May 2007 16:11:40 -0700, Speech Lover wrote: > >> My IVR application records WAV files in a SALT-format of mu-law 8KHz >> 8kbps >> mono, and I need to programmatically convert them to MP3 format for >> another >> application. I searched the Internet for a SDK and found a couple of them >> that might do the work. One is Audio Developer SDK and the other one is >> Audio Format SDK. >> >> Here's the problem: >> When I convert a general WAV file (WAV PCM signed 16bit 16KHz 256kbps >> mono) >> to MP3, no problem! When I convert a WAV file generated from Microsoft >> SASDK, it fails. It appears they complain the same thing - 8KHz sample >> rate >> is NOT supported. >> >> My stupid question is: what makes the difference between Microsoft WAV >> format and a generic WAV format? Is Microsoft WAV format called ACM WAV? >> Could you recommend any MP3 encoder? > > There only is one WAV format, that is the RIFF/WAVE type. However there > are many different types of data that can be placed inside the container, > such as your mu-law data. > > There are various conversion techniques such as ACM, but they only allow > one step conversion. E.g. to convert from mu-law to mp3 you first have to > convert the mu-law to PCM and then to mp3. Depending on what mp3 encoder > you have installed it might not work at 8kHz either. > > In general mp3 is a very poor choice for this type of data, it does not do > well at low bitrates. If your target bitrate is 32kbit ADPCM is a good > choice, below that the speech codecs do best, e.g. Speex, G.729. > > -- > http://www.chrisnet.net/code.htm > [MS MVP for DirectShow / MediaFoundation]

Re: Microsoft WAV vs. Generic WAV "Alessandro Angeli" <nobody[ at ]nowhere.in.the.net> 5/2/2007 7:26:26 PM From: "Speech Lover" [Quoted Text] > Thanks again for your help Chris. > I am able to save files in either PCM format or u-LAW > format. Can you tell me where I can download ACM library > for > conversion of PCM to MP3 so I can give it a try? If WMP7+ is installed (which means WinME/2000/XP/2003 by default, excluding XP-N, and 98/98SE if updated - but I think not Vista), the system already contains an ACM-compatible MP3 encoder, otherwise you need a third-party one (e.g. the ACM wrapper for LAME, if your application's license is compatible with the GPL). Notice that the FhG MP3 encoder included with WMP/Windows may be limited to 56Kbps/24KHz but it is better at low bit/sample rates than e.g. LAME, even though it is considerably slower. -- // Alessandro Angeli // MVP :: DirectShow / MediaFoundation // mvpnews at riseoftheants dot com // http://www.riseoftheants.com/mmx/faq.htm