FreeCalypso > hg > gsm-codec-lib
view doc/AMR-library-tests @ 581:e2d5cad04cbf
libgsmhr1 RxFE: store CN R0+LPC separately from speech
In the original GSM 06.06 code the ECU for speech mode is entirely
separate from the CN generator, maintaining separate state. (The
main intertie between them is the speech vs CN state variable,
distinguishing between speech and CN BFIs, in addition to the
CN-specific function of distinguishing between initial and update
SIDs.)
In the present RxFE implementation I initially thought that we could
use the same saved_frame buffer for both ECU and CN, overwriting
just the first 4 params (R0 and LPC) when a valid SID comes in.
However, I now realize it was a bad idea: the original code has a
corner case (long sequence of speech-mode BFIs to put the ECU in
state 6, then SID and CN-mode BFIs, then a good speech frame) that
would be broken by that buffer reuse approach. We could eliminate
this corner case by resetting the ECU state when passing through
a CN insertion period, but doing so would needlessly increase
the behavioral diffs between GSM 06.06 and our version.
Solution: use a separate CN-specific buffer for CN R0+LPC parameters,
and match the behavior of GSM 06.06 code in this regard.
| author | Mychaela Falconia <falcon@freecalypso.org> |
|---|---|
| date | Thu, 13 Feb 2025 10:02:45 +0000 |
| parents | cc0c244bd233 |
| children |
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The present suite includes a pair of command line programs that exercise libtwamr encoder and decoder in 3GPP test sequence format, allowing this library to be tested against the official test sequences of 3GPP TS 26.074. twamr-tseq-enc ============== This program reads a *.inp file from the collection of TS 26.074, encodes it per selected AMR mode using libtwamr functions, and emits the encoder output in 3GPP-defined .cod format. The command line structure of twamr-tseq-enc is as follows: twamr-tseq-enc [-d] [-2] input.inp mode output.cod The middle argument specifies the codec mode to be used; there is no default. Ordinarily the mode argument is one of these 8 keywords: MR475 MR515 MR59 MR67 MR74 MR795 MR102 MR122 However, this mode argument can also take the form of "file:$modefile", where $modefile is an ASCII text file giving one of the above mode keywords per line. This form is needed when testing the encoding of t21.inp per t21.mod control file. twamr-tseq-enc flag options: -d enables DTX, -2 switches the VAD algorithm from VAD1 default to VAD2 alternative. The two options can be combined as -d2. twamr-tseq-dec ============== This program reads a *.cod file in 3GPP AMR test sequence format, decodes it using libtwamr functions, and emits the decoder output in a raw PCM *.out file. The command line structure of twamr-tseq-dec is as follows: twamr-tseq-dec [-r] input.cod output.out By default the first word of each *.cod frame is expected to be a Tx frame type as in enum TXFrameType; with -r option this first word is expected to be an Rx frame type as in enum RXFrameType instead. This option directly corresponds to -rxframetype in the reference decoder program from 3GPP. Byte order considerations ========================= Both twamr-tseq-enc and twamr-tseq-dec read and write their input and output files (16-bit linear PCM on one end and 3GPP *.cod test sequence format on the other end) in the local machine's native byte order. 3GPP shipped their TS 26.074 collection of AMR test sequences in little-endian byte order; given that most GSM software developers are now largely forced by economic pressures to work on x86 or ARM architecture machines rather than more noble SPARC or PowerPC systems, the local byte order of the developer's machine will typically be LE, matching TS 26.074 files as published.