PhoneSound and wave file formats

Modem compatibility and configuration issues.
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Bill Root
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PhoneSound and wave file formats

Post by Bill Root »

The recent beta versions of Ascendis Caller ID (>= 2.2.0.17) include support for PhoneSound in direct mode (aka TAPI bypass). However, PhoneSound has always been limited in the types of wave files it supports for each modem, whether TAPI is used or not.

Wave files are containers for sampled sound data. The actual format of the sound data within wave files can vary tremendously. (Part of the wave file defines the format of the enclosed sound samples.) Even if the most common unsigned PCM format is used, the number of samples per second and bits per sample can vary from wave file to wave file.

Voice modems support a limited number of sound formats. If the wave file passed to PhoneSound is in a format the modem supports (including number of samples per second and bits per sample) then no conversion is required. In this case the delay in playing the sound will be minimized, and it may sound better than if Windows or Ascendis Caller ID has to convert the file. If the wave file is not in a format the modem directly supports, a conversion is required. Ascendis Caller ID does not support all conversions -- in fact, it only supports a limited number of conversions.

Different voice modems support different sound formats. The formats supported by one of the Zoom 3095 modems I have here are:

Code: Select all

------------------------------
ModemFormatID    : 0
Name             : SIGNED PCM
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 1
Name             : UNSIGNED PCM
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 129
Name             : IMA ADPCM
BitsPerSample    : 4
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 130
Name             : UNSIGNED PCM
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 131
Name             : Mu-Law
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 132
Name             : A-Law
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 133
Name             : 14 bit PCM
BitsPerSample    : 14
SamplesPerSecond : 8000
------------------------------
Of these seven formats, two are the same (1 and 130), and PCM variants (excluding the duplicates) outnumber the other formats 4 to 2.


These are the formats for one of the Zoom 3049C modems in my office:

Code: Select all

------------------------------
ModemFormatID    : 1
Name             : UNSIGNED PCM
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 129
Name             : IMA ADPCM
BitsPerSample    : 4
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 130
Name             : UNSIGNED PCM
BitsPerSample    : 8
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 140
Name             : 2 Bit ADPCM
BitsPerSample    : 2
SamplesPerSecond : 8000
------------------------------
ModemFormatID    : 141
Name             : 4 Bit ADPCM
BitsPerSample    : 4
SamplesPerSecond : 8000
------------------------------
In this case, all are PCM variants, and the same format is duplicated (1 and 130).

(I suspect that all Zoom 3095 modems support the first set of formats and that all Zoom 3049C modems support the second set of formats, but since firmware can be changed, that may not be the case. The 3049C firmware can be user-upgraded; I'm not sure about the 3095.)

If you are recording or generating sound files for use with PhoneSound, your first choice should be to use one of the formats your modem already supports. If you're using pre-existing wave files, it might be worth the effort to convert them beforehand. If you're trying to play a sound through PhoneSound and it doesn't work, try converting the wave file to one of the formats your modem supports directly. In the beta versions at least, the Line Monitor will contain the list of sound formats your modem supports if the modem is opened in direct mode.

Feel free to use whatever sound recording or conversion software you prefer. If you don't have any, one free (but complex) choice is Audacity:
http://audacity.sourceforge.net/


Finest regards,
Bill Root
Ascendis Software
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