Linearity in the regulation of the output level ADAU1701

Hello Piero,

Within its limits, a Sigma eval board can be pressed into yeoman service for impromptu lab work. I've even used one to plot speaker impedance curves and measure distortion. Your project appears to work fine. The LUT values decrease with input, making the pot respond counterclockwise -- I assume that's what you need. Also I can hear a fuzzy noise with headphones at the output. It appears to be caused by the Aux ADC skittering between two of your closely-spaced LUT table entries. In your project the Aux ADCs are set for "No Hysteresis" as shown below:

Unfortunately, this setting really provides 4-bit hysteresis and no LP filtering, which reduces your available resolution at the pot as well as causing the noise. Try the "No Low Pass" setting which actually sets up a LP filter without hysteresis. For the background on this issue, please see this thread:

ADAU1702 hysteresis settings

You'll still need to carefully adjust the pot to bring the Aux ADC output solidly in the middle of the desired LUT "slot" to get a clean output. If you could get by with fewer LUT entries (for example, by including a low-high range switch), this would help. Or you could dispense with the LUT altogether and run the 0 -- 1.0 Aux ADC output directly to the volume control.

Best regards,

Bob

Hello Bob,

thanks for the answer, yes, the pot respond counterclockwise because not to rewrite the table I used one in which I had the counterclockwise operation.

I tried to use the various ways to control the hysteresis, but the differences obtained are very small.

However for what I have to do with this Low Frequency Function Generator. I have no problems that's okay.

It was a curiosity to understand for any project applications which was the best technique for linearly adjusting an audio output.

Piero