3.1 Definitions, symbols and abbreviations

26.0943GPPAdaptive Multi-Rate (AMR) speech codecMandatory speech CODEC speech processing functionsRelease 17TSVoice Activity Detector (VAD)

3.1.1 Definitions

For the purposes of the present document, the following terms and definitions apply:

frame: time interval of 20 ms corresponding to the time segmentation of the speech
transcoder

3.1.2 Symbols

For the purposes of the present document, the following symbols apply.

3.1.2.1 Variables

bckr_est[n] background noise estimate

burst_count counts length of a speech burst, used by VAD hangover addition

hang_count hangover counter, used by VAD hangover addition

complex_hang_count hangover counter, used by CAD hangover addition

complex_hang_timer hangover initator, used fo Complex Activity Estimation

lagcount pitch detection counter

level[n] signal level

new_speech pointer of the speech encoder, points a buffer containing last received samples of a speech frame [2]

noise_level average level of the background noise estimate

oldlagcount lagcount of the previous frame

pitch flag indicating presence of a periodic signal

complex_warning flag indicating the presence of a complex signal.

best_corr_hp normalized and limited value from maximum HP filtered correlation vector

corr_hp filtered best_corr_hp values

pow_sum power of the input frame

s(i) samples of the input framer

snr_sum measure between input frame and noise estimate

stat_count stationarity counter

stat_rat measure indicating stationary

T_op[n] open-loop lags [2]

t0 autocorrelation maxima calculated by the open-loop pitch analysis [2]

t1 signal power related to the autocorrelation maxima t0 [2]

tone flag indicating the presence of a tone

vad_thr VAD threshold

VAD_flag boolean VAD flag

vadreg intermediate VAD decision

complex_low intermediate complex signal decisions

complex_high intermediate complex signal decisions

3.1.2.2 Constants

ALPHA_UP1 constant for updating noise estimate (see clause 3.3.5.2)

ALPHA_DOWN1 constant for updating noise estimate (see clause 3.3.5.2)

ALPHA_UP2 constant for updating noise estimate (see clause 3.3.5.2)

ALPHA_DOWN2 constant for updating noise estimate (see clause 3.3.5.2)

ALPHA3 constant for updating noise estimate (see clause 3.3.5.2)

ALPHA4 constant for updating average signal level (see clause 3.3.5.2)

ALPHA5 constant for updating average signal level (see clause 3.3.5.2)

BURST_LEN_HIGH_NOISE constant for controlling VAD hangover addition (see clause 3.3.5.1)

BURST_LEN_LOW_NOISE constant for controlling VAD hangover addition (see clause 3.3.5.1)

COEFF3 coefficient for the filter bank (see clause 3.3.1)

COEFF5_1 coefficient for the filter bank (see clause 3.3.1)

COEFF5_2 coefficient for the filter bank (see clause 3.3.1)

HANG_LEN_HIGH_NOISE constant for controlling VAD hangover addition (see clause 3.3.5.1)

HANG_LEN_LOW_NOISE constant for controlling VAD hangover addition (see clause 3.3.5.2)

HANG_NOISE_THR constant for controlling VAD hangover addition (see clause 3.3.5.2)

L_FRAME size of a speech frame, 160

L_NEXT length for the lookahead of the speech encoder, 40

LTHRESH threshold for pitch detection (see clause 3.3.2)

NOISE_MAX maximum value for noise estimate (see clause 3.3.5.2)

NOISE_MIN minimum value for noise estimate (see clause 3.3.5.2)

NTHRESH threshold for pitch detection (see clause 3.3.2)

POW_PITCH_THR threshold for pitch detection (see clause 3.3.5)

POW_COMPLEX_THR threshold for complex detection (see clause 3.3.5)

STAT_COUNT threshold for stationary detection (see clause 3.3.5.2)

CAD_MIN_STAT_COUNT minimum threshold after complex warning

STAT_THR threshold for stationary detection (see clause 3.3.5.2)

STAT_THR_LEVEL threshold for stationary detection (see clause 3.3.5.2)

TONE_THR threshold for tone detection (see clause 3.3.3)

VAD_P1 constant of computation for VAD threshold (see clause 3.3.5.2)

VAD_POW_LOW constant for controlling VAD hangover addition (see clause 3.3.5.1)

VAD_SLOPE constant of computation for VAD threshold (see clause 3.3.5)

VAD_THR_HIGH constant of computation for VAD threshold (see clause 3.3.5)

CVAD_THRESH_ADAPT_HIGH constant for updating complex_high

CVAD_THRESH_ADAPT_LOW constant for updating complex_low

CVAD_THRESH_HANG constant for updating complex_hang_timer

CVAD_HANG_LIMIT constant for initiating complex_hang_count

CVAD_HANG_LENGTH constant for resetting complex_hang_count

3.1.2.3 Functions

+ addition

– subtraction

* multiplication

/ division

| x | absolute value of x

AND Boolean AND

OR Boolean OR

MIN(x,y) =

MAX(x,y) =

3.1.3 Abbreviations

For the purposes of the present document, the following abbreviations apply:

ANSI American National Standards Institute

DTX Discontinuous Transmission

VAD Voice Activity Detector

CAD Complex Activity Detection

CNG Comfort Noise Generation