ADAU1701 connect to ADMP441

Hello Jackie,

Yes, as you boost the gain, you will increase the level of all signals. This includes the signal of interest (perhaps a voice or music) and the background noise as well. This is because gain is linear, meaning that it applies to all signals equally.

What is your application? Perhaps it would be better to use a dynamics processor instead of linear gain.

Also, using gain above 1 means that you are lowering the signal to noise ratio of your system (effectively, you are increasing the overall noise level) and you are creating the danger of clipping, which causes severe distortion. So, using gain greater than 0 dB (a linear gain of 1) is not recommended.

hi Brett

I have another sound input through AD channel, the volume is good. The noise is very low. With same system setting, the volume from ADMP441 is very low. So I tried to boost it. I can understand your explanation. But I dont know which dynamic amplifier should be the right choice. My product will record microphone voice, together with the sound from AD channel. I hope the 2 sounds are at same volume, same high S/N. This is very important for us. Please help to find a solution.

Thank you.

Jackie

Another thought, I don't know where the envirnment noise come. Look, I use digital MEMS microphone. It output digital signal through I2S to 1701. I don't think I2S can be polluted by noise. As I mentioned, with same volume, the ADC0/1 gives me a perfect performance. It keeps very quiet when no sound input. Any idea?

Hi Jackie,

What is your input source to ADC0/1? Is it a line input? In this case, the full dynamic range of the input is being used, so of course the noise level will be low.

In the case of a microphone, the full scale input level is very high (120 dB SPL in the case of the ADMP441), so in most standard cases, you be utilizing much less of the dynamic range. This means that the relative noise level will be higher.

Can you describe more about your application? What is the goal of mixing the two signals together?

In order to amplify the region of interest for the voice signal but keep the level from clipping, it probably makes sense to implement some kind of dynamics processor to act as an automatic volume control, like this:

Hi Brett

My application is a recorder, which can record speak voice while a background music playing. They must be at same level volume, or even the voice volume is higher.

I can understand the explanation about dynamic range. But I can not accept it. For example, when ADMP441 is used in mobile phone, the designer has to boost it to a clear volume. But the noise is boosted as well. How can it be used in mobile phone?

I tried the compressor, I can not accept it either. It will output sound suddenly when the input level reached some level. It sounds strainge. And it can not eliminate noise at all. From my perspective, I tried to add a band pass filter before linear amplifier. But the voice quality is not good enough. The noise become dim but still with high level.

Hi Jackie,

Among the things you can try to improve voice quality in your system are the following:

Multiple microphone array to implement a directional resposne

Equalization and bandlimiting

Noise gate

Expander (near the noise gate level)

Compression and limiting to prevent clipping on loud signals

All of these are available on the ADAU1701. However, you will need to tune them for the best performance in your particular application. For that, you might need the help of an acoustics expert or an audio system design consultant. We can help you with the use and configuration of our hardware and software, but when it comes to the tuning of the actual audio system, which is a very complex task, you might need to seek help from an expert in that field.

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Thank you,
EZ Admin