how do I increase output gain at the speaker by 3 to 6 dB with minimal additional noise

Hello,

I loaded your project on a ADAU1761MINIZ board and found that the noise is coming from the programmable gain amplifier (PGA) in the Record signal path -- the 20 dB Boost. I assume you need that boost to get a usable level from your signal source (microphones, etc). Perhaps one or more of the ideas below might help:

1. Place an external low noise analog preamp before the ADAU1761, so you won't need to use the boost.

2. I found that setting the Record signal path controls as shown below -- raising the volume 20 dB while turning off the boost -- resulted in less noise:

3. You could try a dynamic noise reduction scheme like the one shown below. This splits the incoming audio into a dozen 1/3 octave frequency bands, then gates each one ON only if its level is higher than the threshold setting. The idea is to enable only those frequencies with significant signal content. The ones turned OFF can't contribute to the output noise -- reducing the resulting total noise. As a bonus, this technique also helps remove ambient noise picked up by your mics, as long as it's not too loud. I attached the project in case you wish to try it.

4. You'll find a ready-made dynamic noise reducer in the Toolbox under ADI Algorithms. It only works at a 16 KHz sample rate, so it won't help you if you want to keep a higher rate.

Finally, I just discovered that your project specifies a software sample rate (atop the schematic window) of 32 KHz, but a hardware sample rate (in the register controls) of 96 KHz. This mismatch makes your filter frequencies too high by a factor of three, and may introduce other problems. I fixed this in the attached project. For sample rate info, see: FAQ: How do I change the sample rate of my SigmaStudio system? Changing this alone in your original project made it quieter, so I attached this project as well. The original project with an output gain of 8 and the sample rate fix is named w2final2-a; the dynamic noise reduction version is w2final2-b.

Best regards,

Bob

thank you. I think just getting the sampling rates matched helped as

much as anything

You're very welcome. BTW -- We only found the sample-rate mismatch because you had kindly attached your sample project to your question. Problem descriptions alone cannot provide this level of detail. Schematic screenshots, besides often being unreadable, don't show the Hardware Config settings in which your difficulty resided. The project alone contains all the info needed for a resolution. Those concerned about their IP could pare a copy of their project down to the minimum needed to demonstrate the issue in question for submission. This exercise alone may help find the problem!

Questions like yours tend to get answered quickly on EZ. On the other hand, hypotheticals ("Do you think this will work?") and those with incomplete info often sit for weeks here. In effect, anyone choosing to help with these either has to design and build half the system, or else take a best guess -- neither very satisfactory. NevadaMark's excellent blog post -- Asking for Helping Yourself -- provides good advice for any engineer looking for assistance on EZ.

Best regards to all,

Bob