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annotate doc/AMR-EFR-conversion @ 143:195911f2211c

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document PCM format conversion utilities
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 14 Dec 2022 07:04:59 +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
Mychaela Falconia <falcon@freecalypso.org>
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23 give them any special handling, instead they will be bit-reshuffled into MR122
8eb0e7a39409 doc: document command line utilities
Mychaela Falconia <falcon@freecalypso.org>
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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.