Screechy playback after noise removal

[wilki]

Hi,

Initially I had a buzz/hum sound that continued throughout the piece of music I had recorded. I managed to remove this by selecting a silent (except for the hum/buzz) part of the track at the beginning and then using the Noise removal function. I then selected the entire track and applied the same process to delete the hum that runs throughout the track. However, during playback the music is slightly screechy and echoey now. It kind of sounds as though it was recorded underwater!

I have played about with the slider in the Noise Removal drop down, but nothing seems to work.

Anyone had this before? Any ideas would be greatly appreciated. Its driving me mad!

[jan.kolar]

The hum cannot be separated from your music. Only one can 'destroy', so to say, the sound in such a way
that the hum is destroyed much and music only a tiny bit. As far I understand that means
1. lowering the sound volume at moments we think there is no music
2. surpressing some frequencies (tones) where hum/buzz is strong.
If surpress to much music goes away with the hum.
Lowering volume means we either take away a small piece of music or around the music remains
a small piece of hummy echo.
If "2." is done in time dependeng fashion, like "1.", the echoes might be really...

Works well with very small hum.

Be carefull with sliders. Try more conservative setting.

(
Did you read
Noise_Removal http://audacityteam.org/wiki/index.php? ... se_Removal
from
Tutorials http://audacityteam.org/wiki/index.php?title=Tutorials
?. The first paragraph explains better than myself.)


Does anybody please have same examples of what can (cannot) be done with NoiseRemoval
(for http://audacityteam.org/wiki/index.php? ... se_Removal) ?

[wilki]

Thanks for the reply. The buzz/hum is quite noticeable throught the recording so I would probably have to reduce the volume quite alot meaning that there will be a danger of reducing the music's volume too much.

I've tried everything on the wiki hep except for.....

you can also try try going back to the selection chosen for the Noise Profile and reducing its amplification (Effect > Amplify). Then use this as a new Noise Profile. Sometimes running the filter a second time using a Noise Profile that is a de-amplified section of track can give a good result. Another possibility is to select and Edit > Duplicate the track you want to remove noise from before applying Noise Removal, and adjust the relative volume of the two tracks (using the -....+ gain slider on the Track Panel) so you get the best mix of the original and noise removed tracks.

I'll try that tonight.

Any ideas why I have the hum/buzzing sound in the first place. I'm recording from MIXER to AMP to LINE IN on EXTERNAL SOUNCARD to LAPTOP.

The amp is quite old. Could this be the problem?

[steve]

Any ideas why I have the hum/buzzing sound in the first place. I'm recording from MIXER to AMP to LINE IN on EXTERNAL SOUNCARD to LAPTOP.

You've hit the nail on the head. The first thing that you should do if you are getting hum is to try and eliminate it at source. Correcting it after recording is something of a last resort.

The physical cause of the hum is almost always due to poor shielding of signal wires, which then pick up the "hum" of mains electricity (which is present over 100% of the Earths surface), which is then in turn amplified through the signal path.

Some of the most common sources of hum are:

• Turntables
• Musical instruments (for example electric guitars)
• Poor quality leads, or leads of the wrong type
• Missing "Earth" connections
• "Earth Loops"
• Unused inputs left "open"
• Inadequate shielding of one or more pieces of equipment
• Proximity to "noisy" electrical appliances or installations

and the list goes on.

The reason for the problem with turntables is primarily because the signal level from the cartridge is so small that a great deal of amplification is required. For this reason, turntables are often equipped with an "Earthing" point. This usually looks like a screw connection with an "Earth" symbol next to it (http://en.wikipedia.org/skins-1.5/monobook/headbg.jpg)
A wire should be deployed to connect this earthing point on the turntable to a similar point on the amplifier to which the turntable is connected.

With musical instruments, the jack connector is often the culprit. Cleaning or replacing the socket will sometimes fix the problem, but in other cases it is due to the design or build quality of the electronics.

All interconnecting leads must be of the "shielded" type. Speaker leads should not be used for interconnects as they are not shielded. Even cheap shielded cables will usually provide adequate protection, but very cheap, or damaged leads can cause problems.

Avoid placing any audio equipment close to high current appliances, or appliances that use motors (for example, refrigerators, electric fires, fans, air conditioning units...). Also, try to keep input stages away from power amplifiers as they may pick up noise from the large power supply in the power amp.

Check that all mains powered equipment is correctly earthed at the plug. You may read suggestions that the ground pin should be disconnected on some pieces of equipment - for safety reasons you should NEVER do that. In Europe, the "Live", "Common" and "Ground" wires in plugs are clearly colour coded (I'm not sure about the US). Correct wiring is essential for both safety and correct operation and should be checked by a competent person (in some countries the person must be a qualified electrician).

Using different power sockets can sometimes cause problems and may be rectified by plugging all equipment in the audio chain into a multi-way adapter. If you do this you should ensure that the combined current draw does not exceed the power rating for the socket or the adapter.

Laptop power supplies can also be a cause of noise - try running on batteries and see if that is better.

The first thing to do is to try and narrow down the source of the noise.

Set up your equipment so that you can monitor the input signal and turn up the volume sufficiently so that you can hear the hum.
Temporarily turn the volume down and disconnect the sound card, then restore the volume. - Has the hum gone away?
If it has, then the fault is before the laptop, so mute the output again, reconnect the input to the sound card and disconnect the next item in the line (the input to the sound card). Turn the volume back up and check for hum.
Continue this process along the input chain until you have determined how much noise is coming from each stage of the input chain.

Once you have reduced the amount of noise to a minimum, try using Audacity 1.3.5 - the noise reduction effect is different, and in most cases superior to the effect in 1.2.6.

You could also try using my "mains hum filter" plug-in prior to running the noise removal effect - the plug-in is available here: http://easyspacepro.com/audacity/plugins/ and is called MainsHumRemoval.ny
Simply download the plug-in and place it in the Audacity plug-in folder. It will then be listed in your effects menu when you restart Audacity.

[wilki]

Many many thanks for the response Stev.

I'm recording from Turntables and a CD Deck to Audacity.

I'll give some of those suggestions a go tonight. I've got a feeling that it is going to take a while to get to the route of the problem mind. The problem is that the hum isn't really noticable until I have recorded to Audacity. Then during playback it sounds terrible.

I wish my mixer had a line-out so I could go straight to the laptop.

[steve]

Mixers usually have a suitable output. What outputs are available?