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Re: Digital Distortion

Subject: Re: Digital Distortion
From: Walter Knapp <>
Date: Mon, 23 Jun 2003 16:29:08 -0400
Klas Strandberg wrote:
> Hi Walt!
> What you write sounds reasonable, too. Psycho-acoustics is a factor causing
> great difficulties in judging "quality".

When someone talks about the quality of some equipment, I always try to 
judge just how much psycho-acoustics is influencing their experience.

> Yes, I use a 5 year old Pentium. But it is also WaveLab which seems to be
> slow. If I choose the "normal" MP3 process it takes about 2 minutes, "low
> quality" about 30 sec.

My G4 mac is nearly as old, but probably runs rings around yours. I've 
also noted in using windows software it seems less speedy for the same 
processor speed. I certainly spend a lot more time waiting when using 
the Sony laptop, and it's clock speed is 2.5 times faster than my G4. 
This is particularly noticeable when using the same software on each. 
Anyway, the news is that there are combinations of computers and 
software that are pretty speedy.

Unless it's really slow, I don't get all that worried about process 
time. I'm always needing time to just sit back and contemplate what I'm 

> But I'm not so worried about .wav to MP3 conversion, here we all know how
> approximative and risky it is. It's just a way to save file-size.

It was invented and intended to be a way to send soundfiles through the 
internet. That's still it's best use to my mind. It's unfortunate that 
music mp3's introduced the notion of recording them back to CD as if the 
quality was ok.

  It is much
> worse when I don't know - for example - in which order a digital editing
> should be made, to get lowest distortion. 
> I long for some real digitfreak to give me a list, like 1/ First do
> filtering, 2/ then dynamic work, 3/ then noise gates, 4/ finally
> normalizing. Just very practical and straightforward rules! And teaching me
> the errors with doing in another way.

Before starting in to edit stuff for the GA CD, I sat for a whole month 
just trying various filtering options and checking which way to go for 
that material. I do tend to put any equalization before active noise 
removal software as that seems to work better. Dynamic I would tend to 
put in between.

I really think it was worthwhile taking all that time to study the 
problem. I'd probably still be messing with getting the files ready if not.

> I know people who normalize between each step, say, all 10 steps. It appears
> to me to be a dangerous way, but they claim it's okay.

You do have to be careful. My software allows me to stack all the 
filters up as a "superfilter", monitoring the entire combined output. It 
also has small meters between each step. It's surprising how often I 
have to make adjustments between steps to keep the sound levels 
reasonable for good filtering. Otherwise you can end up applying the 
later filters to a very weak signal, or in some cases even clipping 
between sections.

> Anyway, I think too little attention is payed to such "basic" knowledge in
> editing! I mean, most of us need it. 

I think we are still in the early stages of learning filtering for 
nature recording. I read the material on music and so on before 
starting, but so much of it did not apply, or was wrong. Nature 
recording is just enough different.

I think it's also a problem in that each filter plugin behaves a little 
different. With two different major OS's used in the group, we are often 
talking about the same filter, but it's not really the same.

I think we will slowly work out a lot by keeping comparing notes. After 
all, not very long ago it was a total no-no to filter at all in nature 
recording. In fact when this group was formed it was close to that, and 
there are still some members with that mindset. Like it or not, sooner 
or later we all get into it in some way.

> Btw, have you any idea of which MP3 compression that works best with
> birdsong in general? WaveLab gives me 2 options "Lame" and "Fraunhofer". 

I'm more familiar with frogs. The one I use now uses a fraunhofer codex. 
But I have some other fraunhofer based ones that make a mess. The few 
Lame ones I've tried did not do as well as my current software. I think 
it's more finding a particular piece of software that works well. And 
that seems to be trial and error. A lot of the opinion floating around 
does not seem to be based on critical listening.



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