Could anyone has any idea how i could access both channels of sound card at the same time .
Thank you
MATLAB: How to access both channels of soundcard
access both channels of sound card at at the same time
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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.
By setting the "SamplesAcquiredFcnCount" property of the analog output device to be the same as the length of the data being queued, it is almost guaranteed that there will be gaps in the output.
One alternative is to set the "SamplesAcquiredFcnCount" to be less than the length of data being queued, such that data is put into the analog output device queue before the queue is emptied. For example, you may change the previous program in the following manner:
set(ao,'SamplesOutputFcnCount',0.9*datasize);A more reliable option is to use the "TimerFcn" callback. The nature of TimerFcn callbacks is that there is only one of them queued up at any given time. While the SamplesAcquiredFcn callbacks are guaranteed to run, they start taking longer to execute than the frequency with which they are called, and eventually they will queue up and wait.
TimerFcn's on the other hand are discarded if there is already one in the queue. Following is an example that uses the TimerFcn property to achieve continuous analog output. This example uses the Windows sound card via the WINSOUND adaptor:
%%Create ANALOGOUTPUT device and add 1 channel to it (mono)
ao=analogoutput('winsound',0);addchannel(ao,1);%%Configure Analog Output
set(ao, 'BufferingMode', 'Auto')set(ao,'TriggerType','Immediate');%Define output samples per second as necessary
set(ao,'SampleRate',fs);%%configure callback to quuee another chunk of data
% set(ao,'SamplesOutputFcn',{'qmoredata',data});
% set(ao,'SamplesOutputFcnCount',bufsize);
% Use a TimerFcn to queue the next chunk of data
set(ao,'TimerFcn',{'qmoredataForTimerFcn',data});% Set the Timer to fire when 90% of the buffer has been output
set(ao,'TimerPeriod',(bufsize/ao.SampleRate)*0.9);%run the machine
putdata(ao,data);start(ao)% Examine how much data is in the queue.
for ii=1:100 ao.SamplesAvailable pause(1)endstop(ao)% Delete ANALOGOUTPUT object when you are done
delete(ao)clear aoYou may notice that the callback is triggered a little before the buffer runs out of data. It is very important not to starve the running ANALOGOUTPUT object as it will stop and you will notice a discontinuity (or space) between each data output (as in the case of the SamplesOutputFcn used previously). A FOR loop is used at the end of the main program that shows how many samples are available.
The following is example code that illustrates the working of the "qmoredataForTimerFcn" callback (referenced in the code above):
function qmoredataForTimerFcn(obj,event,data) % We would like to make sure we are not going to over run the buffer
% If we do, the PUDATA function become a blocking function
% That is, we will no longer have access to the command line
% Use any ONE of the next two IF statements.
% This one guarantees that we will never get more than twice the amount
% of data we have to queue.
% if (obj.SamplesAvailable + length(data)) >= length(data)*2
% This one will continue to add to the queue until adding more would
% cause PUTDATA to block.
if (obj.SamplesAvailable + length(data)) >= obj.MaxSamplesQueued return end % Else, It is safe to put the data.
putdata(obj,data); % Restart the object only if it is not already running.
if strcmp(obj.Running, 'Off') start(obj) end endIn this example, we look at how many samples are still in the engine's queue and how many we have been requested to add to the queue. If the sum is greater than what we require, we return without queuing more data.
Two criteria can be used to ensure that we do not queue more data that necessary:
1. Twice the length of the data.
2. MaxSamplesQueued.
Note that with the second approach, queueing more data than MaxSamplesQueued will cause the PUTDATA function to block the command line. Therefore, if there is room in the queue, we queue the new data and then restart the object only if it had stopped.
You can tweak the TimerPeriod property and the samples available threshold to suit your particular application and data acquisition device.
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