4.1.2. PrmAGClow_threshold (AGC Noise Level Lower Threshold)

Parameter Number: 0x405

Description: The PrmAGClow_threshold parameter defines the lower threshold for noise level estimates. Any signal above this threshold will be considered speech. Thus, this threshold should be set quite high in order to let the AGC algorithm determine when there are voiced and unvoiced periods. The parameter is given in terms of the average level.

AGClow_threshold is defined as:

• 10^{(output level in dB)/20} * 2²³

Notes:

1. Multiplying by 2²³ converts the value into a linear 24-bit value that accommodates the 24-bit DSPs used on the DM3 boards.
2. The AGC high threshold is determined by the ratio of the PrmAGCk value over the AGCmax_gain value.

Here is a sample calculation to get a hexadecimal value of AGClow_threshold for a noise threshold level of -50 dB_avg:

• 10^(-50/20) * 2²³ = 0x679f

It is recommended that the value be set in the range of -60 dB to -40 dB.

Values: 0x20c5 to 0x3000 (-60 dB to -25 dB)

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