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Re: 60 Hz hum causing problems with speech recognition

In Europe, we call it "the 50-Hz hum" :-)

Tarun, I also vote for a ground loop. You could look if you have more than one device grounded. If you have no grounded devices try to ground the mic-preamp. Usually this helps in our lab.

Good luck,


Pierre Divenyi wrote:
Tarun, you have two options: (1) get rid of the ground loop that is quite probably the culprit, or (2) move to Europe where the 60-Hz hum is unknown.


On 6/16/09 7:43 AM, "Tarun Pruthi" <t.pruthi@xxxxxxxx> wrote:

    Hi all:

    I have been having a lot of problems lately with 60 Hz humming
    noise in my speech recordings (I will confess that most of my
    tests have been on windows/linux laptops - and my guess is that
    they probably have much worse recording quality than desktops on
    average - but we live in a mobile world now and I have to make it
    work on laptops). Whenever it is there, it causes a serious drop
    in speech recognition accuracy, especially since it comes in very
    randomly at times giving for example clean recordings during
    speaker enrollment and noisy recordings in live testing. The
    problem is even worse on linux which has given me all kinds of
    artifacts in the recordings besides the 60 Hz hum - my guess is
    that this is most likely because of driver problems.

    So, I have 3 questions:
    1. What is the source of this 60 Hz noise? Powerline? RF
    interference? I have tried disconnecting the power cord - it works
    sometimes, but not always.
    2. Is there a standard way to get rid of the 60 Hz hum and ensure
    clean recordings for the purposes of speech recognition? The only
    way I can think of is to use notch filters at 60 Hz, and some of
    the harmonics, say 120 Hz and 180 Hz, since most of the times it
    doesn't manifest as a single tone at 60 Hz, but has harmonics all
    over the frequency range.
    3. If this is a well-known problem with sound cards, then why
    aren't we, speech recognition community, trying to come up with a
    mandatory compliance standard for sound card manufacterers which
    ensures that the microphone input is not corrupted by 60/50 Hz
    noise? That should provide a big boost to speech recognition
    accuracies, and a wider acceptance of speech recognition.

    Senior Research Engineer
    Think A Move, Ltd