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I connect aux out from my laptop to USB soundcard mic in and use arecord to record audio. But I am getting noise even recording at CD quality. The nature of the noise is really strange as it seems to vary with the sound. To understand the noise better I played a 440 Hz sinewave and a 200 Hz sinewave to see if the noise remains the same, strangely enough it doesn't. Here is what it looks like .

There is no noise using the same USB soundcard and recording to laptop

Sinewave at 440 Hz

Sinewave at 200 Hz

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    \$\begingroup\$ Can you show the recorded waveform? Is there clipping? \$\endgroup\$
    – CL.
    Commented May 27 at 19:40

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The spectrum indicates the audio output voltage is too high for the recording device audio input and it clips, as the spectrum almost resembles the spectrum of a square wave. You can verify it from the waveform.

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    \$\begingroup\$ +1 There seemed to be a strong correlation between between output frequency and its gain whenever OP was playing said frequency. \$\endgroup\$
    – Colin
    Commented May 27 at 21:08
  • \$\begingroup\$ Great observation, a stupid mistake by me, I didn't notice the volume was too high. \$\endgroup\$
    – Vrisk
    Commented May 28 at 3:44

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