How to remove Noise in ADAU1452

Hello Siva,

What sort of noise are you experiencing? Is it (a) ambient noise picked up by the microphone? (b) Noise (like white noise) generated within the evaluation board? Or (c) acoustic feedback?

If it's white noise originating from the evaluation board, likely it's because the board's inputs are "line level" -- designed for the sort of signals that audio components and headphone jacks of cell phones (etc.) provide. There's no microphone preamps on-board to handle the tiny signals which microphones usually produce. Attempting to load your SigmaStudio project with gain to make up for the low input signal will certainly add noise.

Please share a more detailed description of the issue you're finding.

Best regards,

Bob

Hello Bob,

Thanks for your reply.

Here am experiencing some owl kind of sound. I have attached two schematics (i.e) 1. With Pitch Transposer , 2. Without Pitch Transposer.

If I complied without pitch transposer block there is noise at all, but if I complied with Pitch Transposer am getting some whoo whoo kind of sound.

And the application of our project is voice conversion (Male to Female voice and vice-versa).

Regards

Siva

Hello Siva,

The Pitch Transposer works by recording its input sound into a circular buffer (the "Delay Reserved") at one rate and playing it back at another. The noise you describe results from continuously looping through this buffer. If you increase the Delay Reserved, the buffer cycles less often and the result sounds better. Try 1000 -- 2000 samples -- you have plenty available in the ADAU1452. Also use just enough shift to achieve your desired effect.

Playing a voice podcast through the Pitch Transposer shows it works reasonably well in a voice application. However, if the incoming voice has background noise (hum, air conditioner noise, etc.) it makes the Pitch Transposer's imperfections more evident. Thus, place some voice-specific filtering (get rid of any low-frequency hum as well as high end beyond the useful voice bandwidth) ahead of the Pitch Transposer. Also search Engineer Zone for ideas on how to reduce such noise -- such as building a noise gate or a form of dynamic noise reduction.

Best regards,

Bob

Hi Bob,

Already I have tried Noise gate algorithm but ended with no result. Can you suggest any voice filters as you said?

Regards

Siva

Hi Siva,

Perhaps the Nth-Order Filters would work well here. The higher the order (even numbers only), the better they reject out-of-band signals. Experiment with the lowpass and highpass cutoff frequencies.

Best regards.

Bob

Hi Bob,

As per your suggestion, I tried Nth-Order filter. There is no positive vibes. Same as previous query. If I remove Pitch transposer, there is no noise. If I add am getting noise. I have attached our schematics. Please suggest any algorithm for noise removal or suggest any existed schematics for voice conversion(male to female).

Regards

Siva

Hi Siva,

Developing the algorithm you desire requires deep research into what characterizes male and female voices, then figuring how to implement such a transformation, it possible. It's over my head, and I don't know of any extant algorithms either. I do have an advanced frequency-selective noise gate which does a better job than most. I tried a modification where each frequency channel activates the one an octave higher, thus emphasizing the second harmonic of a voice. This together with the pitch shifter works better than either alone, but it still sounds more like a processed male voice rather than a female one. Below is a section of this circuit:

Best regards,

Bob

Siva,

ADI has developed an advanced noise reduction algorithm of the type that KJBob describes. It can be used alone or in conjunction with Acoustic Echo Cancellation algorithms that pass the highest industry quality standards. We have recently begun demonstrations and evaluations with lead customers.

These algorithm blocks are not included in the standard library because, due to the advanced development and proprietary IP they contain, we are charging licensing fees for these blocks.

If the scale and budget of your project would support negotiated licensing of these libraries, I would be happy to discuss this with you further. Please send me a private message.

Thanks and and best regards,

Ken

Hello Bob,

Thanks for continues help. The above schematics is working fine without any noise.

Regards

Siva

Hi Ken,

Thanks for your involvement towards our project. As per Bob schematics our project is working fine.

Regards

Siva