[TriLUG] Sound Processing

[Neil L. Little]

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.

Neil, WA4AZL
JARS Forever!!


jonc wrote:
> Brian,
>
> 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. )
>>
>>
>> Thanks,
>> Brian
>>     
>
>