view doc/PCM-file-formats @ 282:9ee8ad3d4d30

frtest: rm gsmfr-hand-test and gsmfr-max-out utils These hack programs were never properly documented and were written only as part of a debug chase, in pursuit of a bug that ultimately turned out to be in our then-hacky patch to osmo-bts-sysmo, before beginning of proper patches in Osmocom. These hack programs need to be dropped from the present sw package because they depend on old libgsm, and we are eliminating that dependency.
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Apr 2024 05:44:47 +0000
parents a217a6eacbad
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What file format should be used for 16-bit PCM sample recordings?  The first
(in the order of development) group of utilities in the present package that
need to read and write such files are gsm[e]fr-encode and gsm[e]fr-decode,
designed to mirror amrnb-enc and amrnb-dec from opencore-amr FOSS package;
these utilities read and write WAV files and even use WAV reading and writing
functions copied from opencore-amrnb test code.

However, as I (Mother Mychaela) keep developing more tools, my use cases become
more diverse: in some use cases WAV is most convenient (e.g., when playing or
recording with SoX tools), but in other use cases a raw sample file without any
header is much more convenient.  To address this diversity of use cases, a pair
of conversion utilities have been written:

pcm16-raw2wav converts from raw format to WAV
pcm16-wav2raw converts from WAV to raw format

Both utilities take a mandatory command line argument specifying the endian
order for the raw format - there is no default.

Going forward, I (Mother Mychaela) prefer big-endian format for raw PCM16 files:
aside from it being the network byte order on the Internet, 16-bit and 32-bit
numbers appear "naturally" in hex dumps in BE, but not in LE.  Therefore, newly
developed utilities will read and write PCM16 data in "robe" format - "robe" is
English pronunciation play on "raw BE", and it is also the ritual garment worn
by Themyscira telecom priestesses. :-)