Psmay: Created page with "An '''.ad4''' file is an audio track encoded in a format that can be readily used by low-cost sound modules such as the WTV020* (e.g. WTV020-SD-16P). ==Encoding settings== M..."

2017-06-19T18:54:58Z

Created page with "An '''.ad4''' file is an audio track encoded in a format that can be readily used by low-cost sound modules such as the WTV020* (e.g. WTV020-SD-16P). ==Encoding settings== M..."

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An '''.ad4''' file is an audio track encoded in a format that can be readily used by low-cost sound modules such as the WTV020* (e.g. WTV020-SD-16P).

==Encoding settings==

Most examples of the file format appear to have these properties:

* No header (raw)
* Encoded as VOX/Dialogic/OKI/Intel ADPCM, a lossy but relatively uncomplicated codec with a suitable speed/quality tradeoff for this application
* One channel (mono)
* 32000Hz sample rate (some reports vary)

===Audacity===

[[Audacity]] appears to be able to successfully decode this format based on these settings. (Without the module in hand, not sure whether it can also encode successfully.)

I suspect that the codec is doing something similar to what sox is doing (see below) but silencing the warnings.

===sox===

[[sox]] is able to decode from this format using the '''-t vox''' specification; however, all times I've tried this have resulted in a non-fatal warning to the effect of "ADPCM state errors: ''some large number''". However, the result sounds more or less equal to the result from Audacity.

$ sox -t vox -r 32000 src.ad4 dst.wav
sox WARN adpcms: src.ad4: ADPCM state errors: 14409

When encoding to this format, a clipping warning may appear.

$ sox src.wav -t vox -r 32000 dst.ad4
sox WARN dither: dither clipped 18240 samples; decrease volume?

Ad4 - Revision history

Psmay: Created page with "An '''.ad4''' file is an audio track encoded in a format that can be readily used by low-cost sound modules such as the WTV020* (e.g. WTV020-SD-16P). ==Encoding settings== M..."