How do I switch audio formats?

Last reviewed: 8/21/2001

HOW Article ID: H080106

The information in this article applies to:

SpeechKit 3

Summary

SpeechKit 3 provides you an easy way to switch the audio formats when you need to. For example, if you are generating wave files for playback through telephony systems or other channels that require a different format than the default audio destination multimedia device, then all you have to do is set the AudioFormat property to one of the AudioFormats enumeration values. For example, setting the audio format to 8 kHz 8 bit mono would look something like:


ChantTTS.AudioFormat = AF8kHz8BitMono;

More Information

SpeechKit 3 SR-2 added support for additional audio formats that SAPI5 can convert if the applicable codecs are present on the system. The new formats found in the AudioFormats enumeration are as follows:

AFTrueSpeech8kHz1BitMono
AFCCITTALaw8kHzMono
AFCCITTALaw8kHzStereo
AFCCITTALaw11kHzMono
AFCCITTALaw11kHzStereo
AFCCITTALaw22kHzMono
AFCCITTALaw22kHzStereo
AFCCITTALaw44kHzMono
AFCCITTALaw44kHzStereo
AFCCITTuLaw8kHzMono
AFCCITTuLaw8kHzStereo
AFCCITTuLaw11kHzMono
AFCCITTuLaw11kHzStereo
AFCCITTuLaw22kHzMono
AFCCITTuLaw22kHzStereo
AFCCITTuLaw44kHzMono
AFCCITTuLaw44kHzStereo
AFADPCM8kHzMono
AFADPCM8kHzStereo
AFADPCM11kHzMono
AFADPCM11kHzStereo
AFADPCM22kHzMono
AFADPCM22kHzStereo
AFADPCM44kHzMono
AFADPCM44kHzStereo
AFGSM6108kHzMono
AFGSM61011kHzMono
AFGSM61022kHzMono
AFGSM61044kHzMono

For speech synthesis, if the audio destination multimedia device does not handle the requested format, the format is not changed and reverts back to the original setting. If the format is support by the device, but engine cannot generate the desired format, a return code is returned on subsequent Play method invocations.

For speech recognition, when recognizing from audio data, you only need to set the ChantSR AudioFormat property prior to invoking the Record method if you are passing audio data in a buffers or via an IStream. If passing the data via an audio file, the the recognzier obtains the format directly from the file.