[TriLUG] Sound Processing
Neil L. Little
nllittle at embarqmail.com
Tue Jul 10 22:15:20 EDT 2007
hum in an audio circuit is generally an impedance mismatch. It could
also be a ground loop issue as well.
In the ham radio world this has been a problem when connecting a
computer to a rig (ham talk for radio) for using the digital modes.
I remember seeing in a recent QST magazine (a ham radio magazine)
article about using an audio transformer for isolation to eliminate the hum.
> Do you have any idea what is causing the hum? From your descriptions it
> sounds like a hardware issue (Microphone with too little resistance?)
> Are you applying excessive amplification to the voice?
> We use G729 as our primary codec and that removes a *lot* of
> environmental noise, since it propagates mainly Voice frequencies.Have
> you tried passing the WAV format through various codecs to see if they
> can remove the hum?
> Good Luck - Jon Carnes
> On Tue, 2007-07-10 at 09:48, Brian McCullough wrote:
>> I have an issue that has been causing me a great deal of grief over the
>> past while.
>> I have some sound files ( telephone recordings ) that have a VERY loud
>> 60-Hz hum. They are, at the moment MP3 files, but were WAVs coming out
>> of the recorder.
>> I am wondering if anybody has and bright ideas for inserting a
>> 180 degree out of phase signal to cancel the hum, or any other ideas to
>> clean up these files.
>> ( The hum seems to be being inserted inside my machine, although I am
>> willing to accept suggestions for correcting future meeting recordings,
>> as well as correcting the old recordings. )
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