sound card input and noise cancel

hello i want to cancel some noise of frigirator in my house i want coninously input from sound card and output throw speakers signal with phase -180 what command coniounusly do it all command just record

 y = wavrecord(31250*5,31250);

also is there beter way than sending to speaker -y , i was thinkink about some adaptive filter lms or wiener to cancel the noise in my room

[michael scheinfeild]

i have found somthing in data acquisition but it not work succefuly i think some timing can anybody help , the sound output not synchronized i inveresed the signal

============================

    ai = analoginput('winsound');
  addchannel(ai,1:2);
  set(ai,'SampleRate',44100)
  set(ai,'SamplesPerTrigger',44100)
  ao = analogoutput('winsound');
  addchannel(ao,1:2);
  set(ao,'SampleRate',44100)

for k=1:10
    start(ai)
    wait(ai,3)
    data = getdata(ai);

      putdata(ao,[ -data ])
      start(ao)
  end

delete(ai)
delete(ao)
clear ao

[Walter Roberson]

You are getting one second's worth of samples each time. Your sound is going to have traveled at least 660 feet before you start to output the canceling sound. That has no chance of being useful unless the speaker is at least 660 feet closer to the listener than the microphone is.

[Daniel Shub]

I am not sure that this is true. If the noise is a low frequency periodic hum, for example a compressor motor, then slipped cycles shouldn't be a problem.

[Walter Roberson]

Good point, Daniel.

[michael scheinfeild]

yes it is harmonic noise from pumps tweo floors bentith my apartment it wake me up in the middel of the night i was thinking maybe just sending white noise to the air to cancel this noise

Answer 1

[Walter Roberson]

Sending sounds out of phase 5 seconds after the original sound is not going to achieve any cancellation.

You need to use operations with low latency. The tolerable latency will depend upon the relative distances between the sound source, the microphone, the speaker, and the listener. You will have strong difficulty in getting the microphone latency to less than 6 ms in MATLAB, which is approximately 4 feet of travel for sound (at room temperature). Even getting to 6 ms is not easy, but it is easier as of R2012b (or was it R2012a) which added support for ASIO channels.

You might need the Data Acquisition Toolkit to access the data in nearly those time frames.

Answer 2

[michael scheinfeild]

lets say i want each time to process block of 1024 what is the command for both input and output

[Walter Roberson]

In your code, change SamplesPerTrigger to 1024