Recording output of stereo cable for latency measurement

Hi there,

I have a normal stereo aux cable plugged into the audio input jack. The stereo cable comes from another sound stimulator that produces sounds and sends triggers. The stereo cable contains information of the audiosignal in one channel, and information of triggers in the other channel.

Now I need to measure the latency and jitter of the audiosignal and trigger pulses and ideally I would want to visualise the audiosignal and trigger pulse in a top and bottom graph.

Is there a way to measure and visualise the signals of a stereocable input in Matlab?

[Jonas]

if you want to measure the influence of only the cable itself, consider unplugging it from your device, and plugging both ends into you computer, one in the output, one in the input. you can then send and record simultaneously and look at the lag values. but i doubt that the cable itself will bring much latency in by itself

[Walter Roberson]

Signals travel along wire at 50% to 90% of the speed of light. For discussion we could call it 4 ns/m. Unless you are measuring up past 1/2 GHz you are not going to be able to detect the delay of a 1m cable.

[Anton M]

Hello there, thank you for your comments. My apologies, my question needs some clarification: I am using a raspberry pi as a sound/trigger stimulator and I want to measure is the latency of sound presentation and trigger presentation and compare these latencies. It could be for example possible that sound presentation is slightly delayed (occuring after 3-4ms after trigger presentation due to the soundcard), and I need to measure this exact delay.

In order to measure the resepective delays accurately, I have cut a stereocable and did some soldering to use the left and right channels of the stereocable as inputs for the audiosignal and the trigger.

Left channel: audiosignal from the raspberry pi.

Right channel: trigger pulse from the raspberry pi.

All the grounds were soldered together. The stereocable is then input into my Windows computer and should transmit the the stereo signal with the sound and trigger pulses for analysis.

Thank you for your help!

[Anton M]

https://www.mathworks.com/help/audio/ref/audiodevicereader-system-object.html#d123e58791

I am just looking at the audioDeviceReader function to check if this would be a suitable tool

[Jonas]

are you doing real time processing, then use audioDeviceReader.

if you want just want to do a recording of indefinite length and process the recording afterwards, then i would use audiorecorder()

If i understood you correctly, you want to see the delay between left and right channel since the right channel contains triggers which play audio that is send (after some delay after each trigger) on the left channel.

you can then compare the channels e.g. using crosscorrelation (xcorr()), finddelay() or some kind of thresholding algorithm

edit: let me clearify the first sentence: if you want to find the delay in real time, then use audioDeviceReader

[Anton M]

Thank you Jonas, and yes that is correct. The audiorecorder would be more suitable I think thank you, I will give it a try today!

[Walter Roberson]

dynamic time warping (link: dtw ) might be useful.

[Anton M]

The audiorecorder worked very well thank you!

[Jonas]

great! have a nice day!

Answer 1

[Anton M]

Thank you both, the following worked for me very well!

Fs = 44100 ; 
nBits = 16 ; 
nChannels = 2 ; 
ID = -1; % default audio input device 
recObj = audiorecorder(Fs,nBits,nChannels,ID);

recordblocking(recObj,300);

MyRec = getaudiodata(recObj);

FirstCh = MyRec(:,1);
SecondCh = MyRec(:,2);