Hello,
We are working with the TLV320AIC3106 Codec and have 2 problems with its AGC:
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When calibrating the AGC we found out that its output level (Digital output) is not constant along our audio frequency range (300Hz-3.5KHz). At the high end of the audio range, we achieved the assigned target level; at the low end the output level increased up to 5dB above the target level.
The CODEC assigned to work at 16K samples per second. We are also sampling the digital audio output at 16K samples per seconds and 24 bits per sample.
We designed the AGC to bring the audio signal to half of the full scale, +/- 4E6 (for 24 bits).
We set AGC registers to:
Reg 26 : 0xA3
Reg 27 : 0xA0
We are not using the ADC 1’st order High Pass output digital filter
The audio signal sampled at LINE2L and it is set for differential mode operation.
The signal level inserted is 44 millivolt.
When inserting 1.5KHz signal, the DSP measure 4.1E6 positive and negative peaks.
When inserting 300Hz signal, the DSP measure 6.2E6 positive and negative peaks.
-
Aliasing problem. Even very low level of input signal near 8KHz causes high amplitude “fuzzy” and noisy output signals. Although this frequency is outside of our audio range, some high frequency background signals can cause severe audio interferences.
Please advise us about the potential causes for both problems and preferred solutions. Is the main cause for the 1’st problem related to the AGC averaging method? Is both problems related to the relatively low sample rate that we are using to operate the CODEC?
Best Regards,
Shlomo
