Voice Codecs - GL Communications Inc

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Estimating Speech Quality

The mean opinion score (MOS) is a commonly used method to determine the quality of speech. Every codec has a certain speech quality characteristics. With MOS, the quality of a speech is rated on a scale of 1 (bad) to 5 (excellent).

Recently. the speech quality estimates are based on the ITU G.107 E Model. These models considered the entire Ear-Mouth path and all relevant conditions such as end-to-end level, echo, side tone, and frequency characteristics of the various path segments.

The E Model uses a computational method that includes factors such as noise, signal level, loudness ratings, impairments, delay, codec type, and even network type to derive a quality score. This transmission quality rating is called as the ‘R’ factor. Over time and based on experience with subjective and objective measurements, the E Model's R-Factor score was mapped to an equivalent Mean Opinion Score (Excellent to Bad) to predict the quality of the “mouth to ear” (M2E) speech path. Scoring includes consideration for the type of subjective test used for scoring. Passive/listening or active/conversational tests produce slightly different scores.

For IP networks, the score assumes ideal conditions outside the IP cloud and bases the scores on the relevant IP impairments such as packet loss, latency, jitter, and even when these impairments occur over the duration of the call.

Codec Name Nominal MOS Nominal R factor
G.711 µ-Law (64 kbps) 4.2 93
G.711 A-law (64 kbps) 4.2 93
G.722 (64 kbps) 3.91 96
G.722.1 (32kbps) 4.09 102
G.722.1 (24 kbps) 3.98 98
G.729A/G.729AB (8 kbps) 3.91 82
GSM-FR 3.57 73
GSM HR 3.53 72
GSM EFR 4.16 91
G.726-40k 4.16 91
G.726-32k 4.04 86
G.726-24k 3.35 68
G.726-16k 2.82 57
G.726-40k with VAD 4.16 91
G.726-32k with VAD 4.04 86
G.726-24k with VAD 3.35 68
G.726-16k with VAD 2.82 57
AMR NB Mode 0 (4.75k) (requires additional license) 3.65 75
AMR NB Mode 1 (5.15) 3.73 77
AMR NB Mode 2 (5.9) 3.84 80
AMR NB Mode 3 (6.7) 3.95 83
AMR NB Mode 4 (7.4) 3.98 84
AMR NB Mode 5 (7.95) 4.04 86
AMR NB Mode 6 (10.2) 4.11 89
AMR NB Mode 7 (12.2) 4.16 91
AMR WB Mode 0 (6.6k) (requires additional license) 3.39 81
AMR WB Mode 1 (8.85) 3.81 92
AMR WB Mode 2 (12.65) 4.04 100
AMR WB Mode 3 (14.25) 4.09 103
AMR WB Mode 4 (15.85) 4.11 104
AMR WB Mode 5 (18.25) 4.14 105
AMR WB Mode 6 (19.85) 4.18 107
AMR WB Mode 7 (23.05) 4.18 107
AMR WB Mode 8 (23.85) 4.18 107
EVRC (requires additional license) 3.94 83
EVRCB (requires additional license) 3.98 84
SMV 3.88 81
Speex WB (11.2 kbps) 4.16 106
Speex NB 4.16 91
iLBC 13.3k 3.88 81
iLBC 15.2k 3.95 83

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