Filtering Noise in Audio Signal

Hi guys,
I have a audio signal in u-law format but it has lots of sizzle. Almost all time i can’t hear a sound . Do you have any idea how can i pull clear sound from it ?

how it looks like in audocity

then i apply high pass filter and i can hear little sound

So i am here right now , do you have any suggestion ?

Audacity is not a forensics program. We can’t start from a barely recognizable hash of garbage and pull a voice out of it, particularly if the trash is moving or changing over time.

Two tools that may help are the telephone filter. Effect > Hi Pass Filter set to 300Hz and Effect > Low Pass Filter set to 3000Hz. Audacity 2.1.0 has a telephone preset under Effect > Equalization.

The other one is Noise Removal. Find a portion of the “show” which has noise only and no voice. Drag-select a portion of that and Effect > Noise Reduction > Profile. Then Select a larger portion of the show with voices and Effect > Noise Reduction, 12, 6, 6 > OK.

Noise Reduction (latest version) depends on you being able to find a segment of performance with noise and no show or voice. If you can’t do that, then Noise Reduction isn’t going to work.

Did you try to record the far side of a cellphone or Skype call?


Yes the record is far side of car. When car stops, i can almost hear the voice but when i start driving car noise increasing and i can’t hear anyting.

I think “noise reduction” isn’t fit for me because there is never only noise. I captured another record and show below

Effect > Equalization
i can’t handle this effect , how can i understand which freq I should press

Bass (low) frequencies are on the left, treble (high) frequencies are on the right.
See also: