pops and clicks on ADAU1761 output
I have an ADUA1761 audio codec eval board I'm using for product development. The current setup is simple and is as follows:
1) Rotary encoder attached to GPIO pins 0 and 1, configured using a RotVol1 processing block in SigmaDSP. Works well.
2) Analog output stage implementing differential to single-ended conversion and a ~100kHz low-pass multi-feedback filter. No issues in standalone tests.
3) Input taken from L/R AUX inputs, routed to ADCs, through DSP core and then to L and R differential outputs respectively.
4) All unused inputs/outputs/devices are muted. All volume controls in the CODEC signal path are set to 0dB.
The problem symptoms are straightforward; when playing back signal from a line level source, there are a large number of very loud pops and clicks. These seem to correlate to signal peaks from the source and seems to indicate some sort of clipping. This occurs even when the rotary volume control is set to minimum (taper table value of 0). Altering the ADC and DAC volume control settings in the digital setup menu, does not seem to affect the problem whatsoever. The pops/clicks seem to be much more pronounced when the rotary volume control is set at lower levels but is present throughout the volume taper. The problem does NOT seem to occur when using a lower level input device, i.e. an MP3 player.
Any information as to the cause for this problem and a possible avenue to solve it would be greatly appreciated.
Audio Signal Processors
SigmaDSP Audio Processors
adau1761
What is the full scale voltage level of the signals you have connected to the LAUX/RAUX pins? If you are running the ADAU1761 with AVDD = 3.3V, then the maximum full-scale input is 1.0 V (see "Single Ended Line Input" section of Table 1 in the datasheet). If your signal is exceeding this level, then you will be clipping the inputs, which will certainly result in some unpleasant noises downstream.
The max voltage of the input signal being used is just under 0.9V. Just as a test I've also been able to pass considerably higher that 1.0V PP signals through the ADAU1761 without audibly deleterious effects at the output. With the all of the register settings identical, and just disabling the DSP core, the audio is not passed through the CODEC but identical pops and clicks are present on the output, corresponding to the input signal. Additionally, creating a signal flow linking the inputs directly to the outputs, with no other processing blocks, gives full scale signal at the output without any of the pops or clicks that are present with the volume control in the signal flow. The pops and clicks also seem to disappear when the volume control is set to 100% output.
Could you attach a SigmaStudio project file with a setup that exhibits these clicks? It would be best if we could test this on one of our boards using the same setup that you have.
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Thank you,
EZ Admin
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