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beginning of GSM-HR documentation
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 19 Mar 2026 04:13:45 +0000
parents ebcf414b7d99
children 83de961cc54b
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631:6bad9af66f69 632:7fc57e2a6784
2 ========================================== 2 ==========================================
3 3
4 "TFO transform" is the term adopted by Themyscira Wireless for the non-trivial 4 "TFO transform" is the term adopted by Themyscira Wireless for the non-trivial
5 transform on GSM codec frames called for by the TFO spec, 3GPP TS 28.062 5 transform on GSM codec frames called for by the TFO spec, 3GPP TS 28.062
6 section C.3.2.1.1. We have a goal of implementing TFO transform for all 3 6 section C.3.2.1.1. We have a goal of implementing TFO transform for all 3
7 classic GSM codecs (FR, HR and EFR) in our Themyscira codec libraries; in the 7 classic GSM codecs (FR, HR and EFR) in our Themyscira codec libraries; at the
8 present release, only GSM-FR version has been implemented. 8 present time, only GSM-FR and GSM-HR versions have been implemented so far.
9 9
10 The input to this transform is the stream of received uplink frames from call 10 The input to this transform is the stream of received uplink frames from call
11 leg A, possibly containing BFI frame gaps and SID frames if call leg A uses 11 leg A, possibly containing BFI frame gaps and SID frames if call leg A uses
12 DTXu. The output from the transform is a "pristine" stream of good codec frames 12 DTXu. The output from the transform is a "pristine" stream of good codec frames
13 to be transmitted on the radio downlink for call leg B: good speech frames only 13 to be transmitted on the radio downlink for call leg B: good speech frames only
93 Emission of transform-synthesized SIDs frames during muting states is done in 93 Emission of transform-synthesized SIDs frames during muting states is done in
94 order to help achieve the presumed network operator's goal of DTX maximization 94 order to help achieve the presumed network operator's goal of DTX maximization
95 and radio interference reduction. However, if the input to the transform is 95 and radio interference reduction. However, if the input to the transform is
96 all good speech frames without DTX pauses, the transform does not attempt to 96 all good speech frames without DTX pauses, the transform does not attempt to
97 apply VAD and make its own DTXd. 97 apply VAD and make its own DTXd.
98
99 TFO transform for HRv1
100 ======================
101
102 This transform is implemented in libgsmhr1 in both DTXd=0 and DTXd=1
103 configurations. This feat has been achieved by factoring the Rx front end out
104 of ETSI reference speech decoder, producing a common RxFE block that is then
105 shared by full speech decoder and TFO transform services provided by the
106 library.
107
108 The following articles provide further details:
109
110 HR-codec-Rx-logic Algorithmic logic of ThemWi Rx DTX handler for GSM-HR,
111 shared between the regular speech decoder and our TFO
112 transform.
113
114 HR-codec-library This article describes the API to Themyscira libgsmhr1,
115 the library that implements the present TFO transform
116 along with other GSM-HR codec functions.
117
118 HR-codec-utils gsmhr-tfo-xfrm and gsmhr-tfo-xfrm-dc utilities will be
119 documented here.