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Thread: Trouble with recording line voltage noise

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    Trouble with recording line voltage noise

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    hello,

    I am trying to use audio recorders to record line voltage noise. I essentially step down line voltage noise to a voltage <2V and use the 'Line In' on audio recorders to record it.
    Used a tascam dr-40x and Marantz pmd 561. But what i observed is that tascam does not faithfully reproduce the waveform. see picture below. On the other hand, marantz does a good job(also see picture below).

    Do you guys know what is the difference between the two. why is one doing better vs the other?

    M2-Line voltage
    C2-Playback from recorder
    Attached Thumbnails Attached Thumbnails marantz-playback-vs-line-jpg   tascam-rec-playback-vs-line-jpg  

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    Have you checked the low frequency amplitude and phase response of the recorders?
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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    This is quite a complicated. First of all the transformer doing the step down could be suspect as it could be close to saturation. What is it?

    The waveforms are heavily differentiated resulting in the sawtooth shape, in other word they have been high pass filtered. What does a computer (DAW) 50/60Hz sine look like?

    But then DAWs only give a 'facimile' of a waveshape, they are not like a proper scope. My idea would be to record the mains signal then put it through a Real Time Analyser like Right Mark Analyser the basic form of which is free.

    Or use a hgh pass filter at a few tens of Hz above mains f and just see the noise? A Sallen and Key will give 12dB/octave and if you follow that with another passive stage 18dBoct.

    Dave.

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