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Entry  Fri Jun 3 17:56:14 2016, Varun, Update, General, DAFI update 
    Reply  Tue Jun 7 18:20:18 2016, Varun, Update, General, DAFI update 
       Reply  Wed Jun 8 16:12:38 2016, Varun, Update, General, DAFI update dafi.pngagcin.pdfagcout.pdf
Message ID: 12159     Entry time: Wed Jun 8 16:12:38 2016     In reply to: 12154
Author: Varun 
Type: Update 
Category: General 
Subject: DAFI update 

Summary: I am implementing digital audio filtering on various interferometer signals in order to listen to the processed audio which will help in characterizing and noise reduction in the interferometer. Following is an implementation of an Automatic Gain control (AGC) block on an LSC input signal.

Details of AGC: Currently, the AGC code implemented on FE takes input to fill a frame, then calculates the power in each frame and gives an appropriate gain to it, so that the new power content is to the required level. It is then written to the output, frame by frame. The frame is currently a rectangular window. The frame length and hop size can be adjusted. Current values are as follows:

frame length is 512 samples

hop length is 128 samples.

The input and output are delayed by 1 frame.

Details of testing: Attachment 1 shows a simulink diagram of the DAF system. Eric made this and I modified it later on. Testing was done using signal from the "LSC1" channel. Attachments 2 and 3 show aquired input and output of the AGC respectively. Gain of the preamp of the LSC input signal was varied over a total time span of 200 s. Each gain value was kept for a duration of about 20 seconds. The varying power levels can be seen in the input plot.

The output shows a uniform power level throughout.



Tried to implement AGC on FE. Had some trouble bringing the code into the correct form. It looks okay now. However, this agc code as well as idenntity code (input = output) doesnt seem to build on the c1lsc FE. Have not tried too many debugging steps yet, will come and check the problem tomorrow. 



Wrote and tested a phase vocoder, with two of its applications:

1) Time scaling: This enables change of time duration without affecting the pitch.

2) Frequency warping: This changes the pitch of the sound without affecting the time duration.

1 & 2 tested offline with cavity transmission signal. 1) gives speedup of 2, and 2 gives frequency warping (pitch lowering by a factor of 2)

codes uploaded on github repo



Attachment 1: dafi.png  51 kB  Uploaded Thu Jun 9 17:51:08 2016  | Hide | Hide all
Attachment 2: agcin.pdf  19 kB  Uploaded Sat Jun 11 01:40:33 2016  | Hide | Hide all
Attachment 3: agcout.pdf  21 kB  Uploaded Sat Jun 11 01:41:05 2016  | Hide | Hide all
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