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
(sum
(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.
My McAfee anti-virus anti-malware etc blocked this download …
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
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…
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.
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.
