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doc/Calypso-TCH-downlink: grammar fix
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 20 May 2024 01:24:22 +0000
parents e26b974f7ba3
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1 Historical article from 2023-04
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2 ===============================
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4 The following article was written in 2023-04, a year before the introduction of
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5 libtwamr. All of the utilities described in this article, plus even older
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6 gsm-amr2efr and gsm-efr2amr utilities described in AMR-EFR-conversion article,
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7 are implemented in amrconv subdirectory of the present source package, and are
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8 entirely independent of libtwamr - they predate this library.
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10 Original article follows; the utilities described therein are still useful:
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12 As of this writing (2023-04), the main emphasis here at Themyscira Wireless is
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13 on classic FR and EFR codecs, particularly the latter, rather than AMR.
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14 However, given the close relation between GSM EFR and the highest MR122 mode of
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15 AMR, we are starting to explore AMR a little too, focusing on the reference C
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16 implementation and various published test sequences. Working in this direction,
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17 we have developed the following AMR study and exploration utilities:
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19 amr-cod-parse This utility reads the *.cod binary file format used by 3GPP
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20 reference code and test sequences for AMR-encoded speech, groks
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21 every frame and dumps all recorded parameters in human-readable
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22 form.
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24 amr-ietf-parse A similar AMR parse/dump utility to amr-cod-parse, but reading
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25 the more common IETF RFC 4867 *.amr binary file format instead.
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27 amr-cod2ietf These two utilities convert between 3GPP *.cod and IETF *.amr
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28 amr-ietf2cod formats. amr-cod2ietf converts from *.cod to *.amr;
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29 amr-ietf2cod converts in the opposite direction.
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31 Just like ETSI *.cod and *.dec formats for EFR, 3GPP *.cod format for AMR is
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32 endian-dependent. Our amr-cod-parse and amr-cod2ietf utilities expect LE byte
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33 order by default, matching the official test sequences in
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34 ts_126074v170001p0.zip; they also support BE byte order with -b option.
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35 However, our amr-ietf2cod utility (rarely needed) emits its cod-format output
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36 in the local machine's native byte order.