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annotate doc/AMR-EFR-conversion @ 282:9ee8ad3d4d30

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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 8eb0e7a39409
children 78739fda2856
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8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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1 We have two simple utilities that allow one to experiment with "dumb" bit-
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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2 shuffling conversion between AMR 12k2 and EFR codec formats, to explore
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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3 capabilities and limitations of this approach.
8eb0e7a39409 doc: document command line utilities
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4
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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5 gsm-amr2efr reads an AMR speech recording in RFC 4867 storage format (the common
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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6 .amr format) and converts it to EFR in gsmx format. The AMR input to this
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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7 utility must consists of MR122 frames only - no other AMR modes, no SID and no
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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8 NO_DATA gaps. The intent is that one can take a starting speech sample in WAV
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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9 format, encode it into AMR with amrnb-enc from opencore-amrnb (by default that
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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10 utility produces MR122 encoding without DTX), and then convert the AMR output to
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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11 EFR with gsm-amr2efr. One can then encode the same starting-point WAV speech
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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12 sample with gsmefr-encode (matching official EFR from ETSI) and compare the two
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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13 EFR outputs. When you do this experiment, you will see that the two EFR outputs
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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14 will be different (you can then analyze encoded speech parameter diffs with
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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15 gsmrec-dump), but each version can be fed to an EFR decoder, resulting in
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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16 OK-sounding speech.
8eb0e7a39409 doc: document command line utilities
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17
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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18 gsm-efr2amr performs the opposite conversion: it reads an EFR session recording
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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19 in gsmx format and converts it to AMR storage format. The input to gsm-efr2amr
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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20 is allowed to contain Themyscira BFI markers in addition to EFR frames; these
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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21 BFI markers will be turned into AMR NO_DATA frames. The same input can also
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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22 contain EFR SID frames - however, gsm-efr2amr will not detect them and won't
8eb0e7a39409 doc: document command line utilities
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23 give them any special handling, instead they will be bit-reshuffled into MR122
8eb0e7a39409 doc: document command line utilities
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24 just like EFR speech frames. The result of such "dumb" conversion is invalid
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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25 AMR, and when you decode it with amrnb-dec, you will hear some strange noises.