I had given a sine wave of frequency 2kHz as input to two microphones placed near to each other. The data grabbed by two microphones are then plotted in MATLAB and it was found out that the initial delay of samples between the two microphone was almost 2 samples. When I looked at the complete plot of both the data's in MATLAB the delay was found to be varied. What may be the reason for that.enter image description here

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  • $\begingroup$ How are the two microphones captured? $\endgroup$
    – mmmm
    Aug 12 at 8:40
  • $\begingroup$ Both the microphones are connected to an adc having sampling frequency 40kHz and the data capturing of both the microphones starts at the same time $\endgroup$
    – Deepa
    Aug 12 at 9:20
  • $\begingroup$ by the way, removed "nonlinear" from your title. Nothing in your question is nonlinear. $\endgroup$ Aug 12 at 9:58
  • $\begingroup$ @Deepa bad news: we can, by looking at your plots, determine that sampling does not happen at the same time, or that you're varying your physical setup. One of these has to be the case. $\endgroup$ Aug 12 at 9:59
  • 2
    $\begingroup$ Are these two different ADCs with their own clock each, or are these coupled ADC or two channels on the same ADC ? $\endgroup$
    – Hilmar
    Aug 12 at 11:21

Looks like clock drift.

That happens when you have two independent clocks in the system. Even if they are nominally the same (40 kHz). There will be slightly different and there will be relative drift between them.

Typical audio clocks tend to be within 10ppm of their nominal target. So a drift in the order of 1 sample/second is perfectly normal and expected.

  • $\begingroup$ Won't this drift be a problem in the case of beamforming applications. For example if the two microphones are separated by a distance d, then we expect the data in one microphone will be a delayed version of the other ,where the delay depends on the distance between the microphones. But if the two different microphones connected to two different ADCs having the same sampling frequency will generate a result like above, how to solve the issue $\endgroup$
    – Deepa
    Aug 13 at 11:58
  • 1
    $\begingroup$ Sure. You need to do clock synchronization and/or sample rate conversion. Beam forming must be done using phase-locked clocks. $\endgroup$
    – Hilmar
    Aug 14 at 13:25
  • $\begingroup$ Sir, you were right. This shift between signals was due to drift in clock. $\endgroup$
    – Deepa
    Aug 30 at 9:52

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