How to use DSP algorithm to avoid background noise with SigmaStuido Dev.Tool?

Hello Mia,

Looking at your graph, it looks like a -70dB input will give you an output of appx around -75dB. There is not much compression here, I guess. Is this enough for you? Is there any particular reason that you set it like this.

Please look below I just set that for -100dB output. Try Smoothing out the graph's edges by using soft knee (I didn't use one in the attached pic). Please see if it helps. You can also combine a limiter if needed. I can't see what and all are there in your project since you didn't attach your project.

please see if adjusting the curve helps, also please attach your project with your next reply.

Regards,

Harish

Hello Mia,

Harish has some good suggestions for making adjustments to how the noise gate is working. It will make it a little less noticeable when it turns on and off but in the end it is still a noise gate you are implementing. So once there is a signal present that is above the threshold you will get all of the signal, the desired signal and the noise. Often the desired signal will mask the noise or be so much louder that it does not matter. However, if the desired signal is fairly quiet then the noise will be heard once the noise gate opens up.

There are other techniques you can try. A lot of this will depend on your application. I would like to know what is your end application? A speaker phone? An audio recording system? An intercom?

Then just as important is what is the nature of the background noise you wish to suppress? Is it just hiss from a microphone preamp? Mostly 1/f noise?

What I have seen done and there have been posts on this subject in the forum is to split up the audio band into two or three bands using a crossover block, and then individually implementing a noise gate for each band. That can help a lot sometimes.

You can also get fancier and implement an EQ curve that is level dependent so you roll off the high frequencies less and less until the signal of interest is loud enough to fully mask the noise floor. But this can get a little tricky to implement.

Help us by defining your problem by answering my questions above, then we can better help you.

Dave T

Hello Harish,

Thanks for your suggestions. Whether there are other techniques to suppress the noise when desired signal is present at the same time.

Hello Dave,

Our application is that a Mic input to a Amplified audio output.And the Mic input has 40dB gain as default.

We wish to suppress the noise is the hiss from a microphone preamp.

Here are some spectrograms from our product.

*The Spectrogram when there is no audio to the Mic input:

*The Spectrogram when there is audio to the Mic input:

According to the spectrogram, this noise appears in the full frequency band. We expect that the desired signal is fairly quiet but the noise will not be heard. Whether there are other techniques to suppress the noise whether the desired signal is loud or small.

Hello Mia,

I started this yesterday, got about halfway done and then my entire computer crashed!! Not SigmaStudio, Windows! So I lost my work and had to start over. Got to love Windows!

I wanted to try several different methods of doing this but at the moment, this project only has one. This project uses a crossover to split up the audio band and then sense the level in each band and uses compressors like Harish suggested to make a noise gate. So this will help to reduce noise in a band that is not being used at the moment. See if this helps. I have some test oscillators and I am injecting noise to simulate your -70dB noise floor.

I put in gain reduction meters to show when reduction is happening in each band.

I also setup the limiters to limit the output to a 0dBFS signal to prevent clipping the serial output port and maybe a DAC or other device on the output. But, that very much depends on the device.

Have a look.

ADAU1452 Multiband Noise Suppression.dspproj

Dave T

Hello Dave,

Thank you very much for providing us with a good solution. Let's study it.

Mia