Unwanted noise on recording

[flynwill]

Well that test eliminates grounding as the issue. So it's most likely a fault (or poor design) of your computer's sound card.

A USB headset will probably solve the issue.

[gideon425]

I increased the value of Capture as much as possible but it did not make any significant difference to the hum

[Trebor]

I increased the value of Capture as much as possible but it did not make any significant difference to the hum

If it worked it would reduce level of hiss relative to the signal, it would not reduce hum.

Here's a digital solution to removing your mains-hum ...
Paste the code below into something called "Nyquist Prompt" (in Audacity Effects Menu )

Code: Select all

(setf s (notch2 s 450 25)) 
(setf s (notch2 s 400 25))
(setf s (notch2 s 350 25))
(setf s (notch2 s 250 25))
(setf s (notch2 s 200 25))
(setf s (notch2 s 100 25))
(setf s (notch2 s 50 1))

So it looks like this ...

Nyquist Prompt with code pasted in.gif (9.8 KiB) Viewed 1630 times

Then apply "Nyquist Prompt " like any other Audacity effect ...

''xx'' before-after Code shown applied to remove mains-hum ( has no effect on hiss ).wav

(1015.63 KiB) Downloaded 88 times

NB: this will only remove hum , it makes no difference to the hiss.

PS the spectrogram of your "xx" hum example is consistent with an electrical-hardware problem called "impedance mismatch", i.e. you need to try a different microphone to get better sound into that computer.

[gideon425]

I have been using the "noise removal" option in Audacity, selecting a few seconds of sound where I do not speak, to guide the removal process. This seems to work very well as the noise is almost completely gone.

It would be nice if there was an application I could run to sit between me and the SIP client, filtering out the noise.

[Trebor]

It would be nice if there was an application I could run to sit between me and the SIP client, filtering out the noise.

Many computer sound-cards do have real-time noise-reduction, aka "Noise Suppression", as one of their "enhancements".

[gideon425]

My card is HDA Intel (chip VIA VT2020)

There is some information here but it does not mention noise reduction
http://www.via.com.tw/en/support/tech_faq.jsp

The normal command I use to access the card is alsamixer. When I run this command, I do not see any noise reduction option to enable

[Trebor]

Like I said I'm not fluent with Linux so , you'd have to Google real-time "noise suppression" ubuntu.