[TriLUG] Sound Processing

[Neil L. Little]

Ok, I found the article...June 2007 QST, issue p59. Audio isolation can 
be achieved with just a $4 1:1 audio transformer radio shack part # 
273-1374.
This should eliminate the hum you are experiencing when recording.

Neil, WA4AZL
JARS Forever!!


Neil L. Little wrote:
> 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
>>>     
>>
>>