Audio distortion issue (low frequencies are boosted)

[Noob@Audio]

Hi All,

This may be a bit of a long shot, but I am working on a system which has a DSP generating 3 frequency tones @ 400, 800 and 1600 Hz via a codec (TLV320AIC3106) this is picked up by a microphone via another codec (SGTL5000) and an fft is done on the recorded signal.

99% of the time there are 3 peaks in the fft at the correct frequencies with consistent amplitudes.

The other 1% of the time the peaks detected are ~20Hz off the target frequencies and the amplitude of the ~400Hz signal is 3x what it normally is, the amplitude of the ~800Hz signal is about normal and the ~1600Hz signal is sometimes not present, or if it is, the amplitude is lower again.

Once the issue occurs once, it seems to happen each time the test is run until power is removed for a period of time, and then the system goes back to functioning normally.

Has anyone experienced this sort of distortion before? I can't share much more details unfortunately but I am hoping that someone can suggest a likely cause, as the issue very consistently exhibits the described features.

Thanks,
Graham

 

[Holmz]

That DSP sounds like it has a bug.

 

[fastfreddy666]

On page 29 of the spec sheet: "It is recommended that the digital effects filters should be disabled while the filter coefficients are being modified. While new coefficients are being written to the device over the control port, it is possible that a filter using partially updated coefficients may actually implement an unstable system and lead to oscillation or objectionable audio output. By disabling the filters, changing the coefficients, and then re-enabling the filters, these types of effects can be entirely avoided." (1)

In other words. You're probably doing something wrong. We are only human. Don't blame the chip.

(1) https://www.ti.com/lit/ds/symlink/t...81779&ref_url=https%3A%2F%2Fwww.google.com%2F

 

[Noob@Audio]

On page 29 of the spec sheet: "It is recommended that the digital effects filters should be disabled while the filter coefficients are being modified. While new coefficients are being written to the device over the control port, it is possible that a filter using partially updated coefficients may actually implement an unstable system and lead to oscillation or objectionable audio output. By disabling the filters, changing the coefficients, and then re-enabling the filters, these types of effects can be entirely avoided." (1)

In other words. You're probably doing something wrong. We are only human. Don't blame the chip.

(1) https://www.ti.com/lit/ds/symlink/tlv320aic3106.pdf?ts=1643105081779&ref_url=https%3A%2F%2Fwww.google.com%2F

Thanks Freddy, that was fast

I don't enable the digital effects or change the filter coefficients, I shall investigate if it is being done accidently.

 

[raindance]

Perhaps you left some pins floating that require termination.