Buzzing noise on captured video

[kefoo]

Hi! I captured some video direct from TV a while back. When I went to edit it I discovered the entire video had a constant high pitched buzzing noise like you can sometimes hear from a TV or monitor. Is there a utility I can use to clean this up without completely destroying the audio?

Kefoo

[Sciascia]

If you can find a spot of just pure noise and it is a constant pitch, you can try to phase shift it and combine it to the same channel (not necessarily same track) it should help to cancel out the noise. If not maybe there are some audio filters in your editing app.

[Marijn]

Cooledit is available as a demo application that has limited functionality. But at no cost it will be able to remove (constant) noise patterns just by analyzing a silent part, where only the noise is present. This works rather well.

Your noise is probably the cause of undersampling. If your audiosignal has frequenties up to 15kHz (like most TV-interference), recording with more than twice this frequency (more than 30kHz) will usually give no problems. If you lower the sampling rate to let's say 22kHz, since no more is needed, the input signal has to be limited to 11kHz (22*0.5). If I'm correct, a signal with a frequency of 15kHz that is sampled at 22kHz will be recorded as a 7kHz frequency (very anoying). As you can see this is the difference between 15kHz and 22kHz.

One would assume that the hardware of the soundcard would filter out all higher frequencies, but as I discoverd myself this is not always true. For me it is only 44kHz samplingrate nowadays...

Happy editing,

Marijn

[Dr Mordrid]

A buzzing can also come from a ground loop in the computer system.

You can also get buzzing from flourecsent or halide lamp transformers that emit RF that leaks into the audio cables.

Another source can be an overmodulated video signal. This often happens with signals whose characteristics cause the overmodulated video to bleed into the audio signal. The classic example is the weatherman with a black & white checked or striped jacket.

Dr. Mordrid


[This message has been edited by Dr Mordrid (edited 21 November 2000).]