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Suppressing buzz

 
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normloomer



Joined: 11 Nov 2006
Posts: 17

PostPosted: Tue Dec 16, 2008 1:38 am    Post subject: Suppressing buzz Reply with quote

I ask for your help, but also your patience, because I am ignorant
about audio, but I have a problem that Ia friend has asked me to work
on.

He recorded a video of the memorial service for a mutual friend. The
audio recording has a serious buzz, which may have resulted from
plugging the camera into a wall outlet. The buzz overwhelms the spoken
audio.

I have looked at the documentation for Amadeus II and Amadeus Pro and
do find that this topic is mentioned, but not in enough detail to be
helpful to this neophyte. I think that what I want to do is to isolate
the frequency of the hum and suppress it using Effects > Denoising >
Suppress Frequency Band. I used Analyze > Spectrum and found spikes at
about 63Hz and 180Hz. (This was a surprise, as I was expecting a spike
at 60 Hz (U.S. electrical system)). Then I tried Effects > Denoising >
Suppress Frequency Band on frequencies around each of those spikes. I
set Lower Frequency and Upper Frequency to bracket each frequency
spike in turn. I didn't know what to do with Transition Width, as it's
not mentioned in the documentation. I played around with the settings
as I previewed the resulting sound, but was not able to suppress the
buzz at either frequency.

I also tried Effects > Denoising > Sample Noise / Suppress Noise,
Effects > Denoising > Suppress White Noise and Effects > Denoising >
Supress Low Frequencies. (Those may have been totally inappropriate,
but that highlights my level of ignorance).

Is this problem solvable? Would someone be willing to hold me hand and
walk me through this?

-Norm Loomer
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CDJonah_alt



Joined: 15 Mar 2007
Posts: 378

PostPosted: Tue Dec 16, 2008 2:44 am    Post subject: Suppressing buzz Reply with quote

After you did the filtering, was the intensity lower at 63 and 180 hz?
If not, your filtering wasn't good.

60 and 180 are common because they are first and third harmonics. I
would also expect 5 and 7 also.

Do you have a section of sound where there is no real signal?

Chuck

Norm Loomer wrote:
Quote:
I ask for your help, but also your patience, because I am ignorant
about audio, but I have a problem that Ia friend has asked me to work on.

He recorded a video of the memorial service for a mutual friend. The
audio recording has a serious buzz, which may have resulted from
plugging the camera into a wall outlet. The buzz overwhelms the spoken
audio.

I have looked at the documentation for Amadeus II and Amadeus Pro and
do find that this topic is mentioned, but not in enough detail to be
helpful to this neophyte. I think that what I want to do is to isolate
the frequency of the hum and suppress it using Effects > Denoising >
Suppress Frequency Band. I used Analyze > Spectrum and found spikes at
about 63Hz and 180Hz. (This was a surprise, as I was expecting a spike
at 60 Hz (U.S. electrical system)). Then I tried Effects > Denoising >
Suppress Frequency Band on frequencies around each of those spikes. I
set Lower Frequency and Upper Frequency to bracket each frequency
spike in turn. I didn't know what to do with Transition Width, as it's
not mentioned in the documentation. I played around with the settings
as I previewed the resulting sound, but was not able to suppress the
buzz at either frequency.

I also tried Effects > Denoising > Sample Noise / Suppress Noise,
Effects > Denoising > Suppress White Noise and Effects > Denoising >
Supress Low Frequencies. (Those may have been totally inappropriate,
but that highlights my level of ignorance).

Is this problem solvable? Would someone be willing to hold me hand and
walk me through this?

-Norm Loomer
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anechoic



Joined: 01 Nov 2008
Posts: 60
Location: San Francisco

PostPosted: Wed Dec 17, 2008 10:15 pm    Post subject: Re: Suppressing buzz Reply with quote

normloomer wrote:
I used Analyze > Spectrum and found spikes at
about 63Hz and 180Hz. (This was a surprise, as I was expecting a spike
at 60 Hz (U.S. electrical system)).

the resolution of the Spectrum's time axis is not adjustable - so looking at it in full view you won't be able to mouse over a freq with any accuracy.

Another thing to add to my wish list!

normloomer wrote:
The buzz overwhelms the spoken
audio.

if the buzz overwhelms the dialog then there is probably not much you will be able to do with the noise reduction tools in AP.
The artifacts you create with NR will be worse than the buzz.
if it's any consolation: this a painful lesson we all learn the hard way!
Smile


Last edited by anechoic on Wed Dec 17, 2008 10:33 pm; edited 1 time in total
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normloomer



Joined: 11 Nov 2006
Posts: 17

PostPosted: Wed Dec 17, 2008 10:16 pm    Post subject: Suppressing buzz Reply with quote

On Dec 15, 2008, at 8:44 PM, Charles Jonah wrote:

Quote:
After you did the filtering, was the intensity lower at 63 and 180
hz? If not, your filtering wasn't good.

Yes, in the initial try but not at 63 later. (See below.)

Quote:
60 and 180 are common because they are first and third harmonics. I
would also expect 5 and 7 also.

I found those harmonics and several more odd-numbered ones as well as
some even-numbered ones.

Quote:
Do you have a section of sound where there is no real signal?

Yes, I have a section that contains only buzz. I am using it as the
basis for choice of frequencies that I try to suppress.

I have reduced the buzz somewhat, but the spoken audio is still
obscured. With one exception, I have been able to suppress the
frequencies that I've tried. The exception is a strong spike (-23.5
dB) at 63.05 Hz. (Curiously, there was no spike at 60 Hz.) I've tried
bracketing that frequency with the interval (62.5, 63.5) in Effects >
Denoising > Suppress Frequency Band, but it persists.

I am beginning to think that the audio is so deeply buried in buzz
that it can't be recovered.

-Norm Loomer

P.S. I still don't know what Transition Width means, and don't know
how I should be setting it.
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CDJonah_alt



Joined: 15 Mar 2007
Posts: 378

PostPosted: Wed Dec 17, 2008 10:50 pm    Post subject: Suppressing buzz Reply with quote

If the signal is well below the noise, it can be very difficult to do
much; yes they can do it on television, but not so much in the real world.

take a section that only has noise and select it.

Go to the denoising menu and select "sample noise"

Then go back and select The whole signal and use "suppress noise" --
see if that helps -- there is in the same menu and item called
"settings". You can play with those.

If I remember correctly, this uses a form of optimal or Wiener filtering
where you basically remove the frequency spectrum of the noise from the
signal.

Chuck

Norm Loomer wrote:
Quote:

On Dec 15, 2008, at 8:44 PM, Charles Jonah wrote:

Quote:
After you did the filtering, was the intensity lower at 63 and 180
hz? If not, your filtering wasn't good.

Yes, in the initial try but not at 63 later. (See below.)

Quote:
60 and 180 are common because they are first and third harmonics. I
would also expect 5 and 7 also.

I found those harmonics and several more odd-numbered ones as well as
some even-numbered ones.

Quote:
Do you have a section of sound where there is no real signal?

Yes, I have a section that contains only buzz. I am using it as the
basis for choice of frequencies that I try to suppress.

I have reduced the buzz somewhat, but the spoken audio is still
obscured. With one exception, I have been able to suppress the
frequencies that I've tried. The exception is a strong spike (-23.5
dB) at 63.05 Hz. (Curiously, there was no spike at 60 Hz.) I've tried
bracketing that frequency with the interval (62.5, 63.5) in Effects >
Denoising > Suppress Frequency Band, but it persists.

I am beginning to think that the audio is so deeply buried in buzz
that it can't be recovered.

-Norm Loomer

P.S. I still don't know what Transition Width means, and don't know
how I should be setting it.

--
Charles D. Jonah CDJonah@anl.gov
630-252-3471
Chemistry Division
Argonne National Laboratory
Argonne, IL 60439



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