Help to fix an audio file?

Hello everyone.

I have a 10 minutes phone call that was recorded with a hand-held digital recorder.

The problem is that some noise, interference sound came through when the recording was silent (when no voice was being recorded).

I have tried to the best of my knowledge (and comprehension of the noise removal tutorials) to sort this out, but did not have success yet.

In the following link you can download this audio file. It’s only 5mb, really small.

Can someone please shed some light over this problem, a way that can solve it?

Or maybe help me do it? It is really important to have it sorted out, so I’m willing to do whatever it takes to get it right.

Thanks everyone.

That recording is so badly damaged that there is not a great deal that can be done.
However, using Audacity 1.3.12, try this:

Open the file and select from the Effect menu “Nyquist Prompt”.
In the Nyquist Prompt text box, copy and paste the following code, then press the OK button.

(scale 0.5 
  (highpass8 (lowpass8 (notch2
      (aref s 0)
      (mult -1 (db-to-linear 7.3)(aref s 1)))
    1415 1) 5000) 400))

Nyquist effects are fairly slow, so you may want to try it out on a short section first.
Let me know how you get on.

if the noise is only when they are not talking
you can cut out those sections
or silence them by amplifying by large negative value

My McAfee anti-virus anti-malware etc blocked this download …
McAfee warning Re megaupload.PNG
Here is an excerpt from Call1.WAV, which I have scanned for nasties (using McAfee and MBAM) …

The pulsing sound EMI sound is not confined to “silence”. Good luck trying to remove it, you’ll need it

Here’s a short section in WAV format.

Thanks everyone.

I’ll try these ideas now and come later with some updates.

Do you have any idea of why that sound emerged in the recording?

I have some ideas, perhaps they have influenced: 1) I had a TV set on nearby (on mute sound); 2) I had a Wifi router nearby (on); 3) I recorded this on ST HQ (Stereo), but the sound was coming from a single channel loud speaker.

Do you agree that using Mono HQ instead of Stereo HQ will work best for this? I’m recording from a phone loud speaker, so it’s coming out from a single channel…

Thanks a lot.

It is much better already, the noise is left more in the background and the voice is even clearer.

Here’s a 30 sec sample of how it looks now:

Any further ideas?

Can’t thank enough!

I’ve had a go …

The pulses have a fundamental frequency of 108Hz and I applied variable de-hummer at that frequency.
It doesn’t really improve the intelligibility though.

The sound (which you couldn’t hear at the time) is EMI, sounds like that produced by the mobile phone radio transmission.

Thanks a lot!

Hummm… it could be.

Any idea of how to avoid that for next time?

I was using a mobile phone with Wifi turned on (for no reason), recording was on Stereo channels L and R.

An aluminium/ aluminum/kitchen foil shield may help with a 5-10mm hole in it to let the sound reach the mic.

Don’t permit the foil to touch anything metal, [If you get electrocuted sue Kozikowski it was his suggestion].

Hey what about a dud CD/DVD a shield: they’re coated with Aluminium and have a hole in the middle for a mic.

Cellphones negotiating a connection of any sort can interfere with sound production. I was doing a simple voice capture and no matter what, I got odd sounds mixed in with the voice, and we were in an electrically quiet room. “Where,” I said, “is your cellphone?”

I didn’t have mine with me.

He pulled out his Motorola which was trying frantically to establish a connection in our cellphone challenged neighborhood. Turn that off and poof, no more problem.

<<<Hey what about a dud CD/DVD a shield:>>>

You need to form a Faraday Shield around the device --wrap it like a burrito – and no hole can be larger than quarter wave at the interfering frequency.


the number one rule for home studios
all cellphones in the house off
amongst other noise inducing gadgets