40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Wed Oct 24 14:15:34 2012, Ayaka, Update, Adaptive Filtering, microphone noise mic_open.pngmic_noise.png
    Reply  Wed Oct 24 15:29:52 2012, rana, Update, Adaptive Filtering, microphone noise 
       Reply  Wed Oct 24 17:02:01 2012, Jenne, Update, Adaptive Filtering, microphone noise 
       Reply  Wed Oct 24 22:20:24 2012, Den, Update, Adaptive Filtering, microphone noise mic_64k.pdf
          Reply  Thu Oct 25 09:53:23 2012, Ayaka, Update, Adaptive Filtering, microphone noise 
          Reply  Thu Oct 25 10:03:38 2012, rana, Update, Adaptive Filtering, microphone noise 
             Reply  Thu Oct 25 14:39:14 2012, Den, Update, Adaptive Filtering, microphone noise 
Message ID: 7621     Entry time: Thu Oct 25 09:53:23 2012     In reply to: 7614
Author: Ayaka 
Type: Update 
Category: Adaptive Filtering 
Subject: microphone noise 

Quote:

Quote:

  We have to change the sample rate and AA filter for the mic channels before going too far with the circuit design.

 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.

 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?

ELOG V3.1.3-