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Wed Oct 24 14:15:34 2012, Ayaka, Update, Adaptive Filtering, microphone noise 
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Wed Oct 24 15:29:52 2012, rana, Update, Adaptive Filtering, microphone noise
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Wed Oct 24 17:02:01 2012, Jenne, Update, Adaptive Filtering, microphone noise
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Wed Oct 24 22:20:24 2012, Den, Update, Adaptive Filtering, microphone noise
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Thu Oct 25 09:53:23 2012, Ayaka, Update, Adaptive Filtering, microphone noise
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Thu Oct 25 10:03:38 2012, rana, Update, Adaptive Filtering, microphone noise
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Thu Oct 25 14:39:14 2012, Den, Update, Adaptive Filtering, microphone noise
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Message ID: 7621
Entry time: Thu Oct 25 09:53:23 2012
In reply to: 7614
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Author: |
Ayaka |
Type: |
Update |
Category: |
Adaptive Filtering |
Subject: |
microphone noise |
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Quote: |
Quote: |
We have to change the sample rate and AA filter for the mic channels before going too far with the circuit design.
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PEM model is running at 64K now. It turned out to be tricky to increase the rate:
- BLRMS are computationally expensive and original pem model did not start at any frequency higher then 16k ( at 16k cpu meter readings were 59/60 ). Also when we go higher then 16k, front-end gives the model less resources. I guess it is assumed that this model is iop and won't need too much time. So in the end I had to delete BLRMS blocks for all channels except for GUR2Z and MIC1.
- Foton files are modified during model compilation: lines with sampling rate and declaration of filters in the beginning of the file are changed only. Sos-representation and commands are the same. I hoped that filter commands will let me change sos-representation quickly. I've opened Foton and saved the file. However, Foton modified commands in such a way that the ratio of poles and zeros to sampling rate is preserved. I guess all filters have to be replaced or this process should be done in another way.
- BLRMS block uses low-pass filters below 0.01 Hz, increasing the sampling rate by a factor of 32 might make calculations incorrect. I'll check it.
We should also increase cut off frequency of the low-pass filter in the microphone pre-amplifier from 2 kHz up to ~20-30 kHz.
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Thank you for changing the sample rate!
Also we have to change the Anti-Aliasing filter, as Jamie said.
Now my question is, whether S/N ratio is enough at high frequencies or not. The quality of EM172 microphone is good according to the data sheet. But as you can see in previous picture, the S/N ratio around 1kHz is not so good, though we can see some peaks, e.g. the sound that a fan will make. I have to check it later.
And, is it possible to do online adaptive noise cancellation with a high sampling rate such that computationally expensive algorithms cannot be run? |