FreeCalypso > hg > gsm-codec-lib
comparison doc/HR-codec-limits @ 632:7fc57e2a6784
beginning of GSM-HR documentation
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Thu, 19 Mar 2026 04:13:45 +0000 |
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| 631:6bad9af66f69 | 632:7fc57e2a6784 |
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| 1 GSM-HR speech codec is currently deemed by us to have no practical utility: | |
| 2 | |
| 3 * GSM networks that need to use half-rate channels for capacity reasons will | |
| 4 preferentially use AMR-HR (superior speech quality to HRv1), and may even | |
| 5 have to reject GSM MS that don't support it; | |
| 6 | |
| 7 * GSM networks that aren't so constrained in capacity will use one of AMR-FR, | |
| 8 EFR or FRv1, all of which provide better speech quality than HRv1. | |
| 9 | |
| 10 Because of this lack of practical utility, some important limits have been | |
| 11 placed on the scope of work to support this codec in the present Themyscira | |
| 12 Wireless GSM codec libraries and utilities suite: | |
| 13 | |
| 14 * Between speech encoder & decoder functions on the one hand and the TFO | |
| 15 transform function (TS 28.062 section C.3.2.1.1) on the other hand, the | |
| 16 latter received more development attention. For completeness, TFO transform | |
| 17 implementations need to be provided for all 3 codecs for which this transform | |
| 18 is defined, and the implementation of TFO transform for GSM-HR serves as a | |
| 19 stepping stone toward the much more important one for EFR. | |
| 20 | |
| 21 * Librified forms of speech encoder and decoder engines from GSM 06.06 GSM-HR | |
| 22 reference code have been included in libgsmhr1 for the sake of completeness, | |
| 23 as well as command line utilities built on top of these library engines. | |
| 24 However, unlike the situation with EFR and AMR codecs, no effort is being | |
| 25 expended to make these operations fast or computationally efficient - the | |
| 26 slow and grossly inefficient code from ETSI remains mostly unchanged except | |
| 27 for elimination of global variables and introduction of state structures. |