Re: arsclist Re: Thoughts...

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 07/12/02, Alyssa Ryvers wrote:
> I am not a big fan of noise reduction either - you can't remove the
> "noise" without changing the sound of the room it was recorded in. As
> a recording engineer, my interest is to find the appropriate room; it
> greatly effects the recording. 

> Today, when I took my "noise sample" from a recording I am mastering,
> I am also sampling, in this "quiet spot", the room ambience. Noise and
> room come down together, when I apply the noise reduction.

Let's distnguish between random noise (hiss) and impulse noise (clicks).
Both have an even frequency response, so frequency-based filtering (such
as low pass filters) is no use.

A 78 has a high level of hiss _and_ millions of clicks. The clicks occur
at random times and last for a very short time (the better the pickup
cartridge, the shorter the time).

You can think of the signal as alternating between (hissy) music and
clicks. The clicks take up less time than the music.

In general, it should be possible to detect and remove the great
majority of clicks without affecting the music or reverberation, because
there is enough information about the music on either side of each click
to allow restoration.

Removing hiss without affecting reverberation or the dying away of a
note on a piano is much harder. It can be done to a limited extent but
with current technology, there are undesirable side effects. Where the
original has only a little hiss, as with a studio quality analogue tape,
it can be successful. Where there is a lot, as with 78s, you have a
problem.

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx

-
For subscription instructions, see the ARSC home page
http://www.arsc-audio.org/arsclist.html
Copyright of individual posting is owned by the author of the posting and
permission to re-transmit or publish a post must be secured
from the author of the post.