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Re: Headroom for processing

Subject: Re: Headroom for processing
From: "Raimund Specht" <>
Date: Wed, 25 Jun 2003 17:24:06 -0000
Walter Knapp  wrote:

> Raimund Specht wrote:
>   However, if the
> > original noise floor has been removed by applying a noise gate 
> > filter (or even by the inherent noise gate effects of ATRAC / 
> > compression algorithms?), this kind of distortion could become 
> > audible. 
> You continually assume things about ATRAC, something you have not 
> have not even limited experience with. Please refrain from talking 
> things you know nothing about like this. You do not need to 
> such misinformation into every discussion.
> Stick with mp3, and even there just the particular codex you know.
> Walt

I'm afraid, that this is no misinformation. It is a fact, that both 
ATRAC and MP3 may reduce the bit depths in frequency bands, that are 
masked by louder sound components (known as "bit depth allocation"). 
According to the ATRAC specification, this bit depth allocation may 
also lead to zero bits. This means, that low-amplitude signals (e.g. 
noise) can be removed completely from a certain frequency band. This 
effect would correspond to a noise gate. I have seen that many times 
in both MP3 and ATRAC recordings. However, the degree of this effect 
may of course depend on the specific implementation of the encoder. 

I mentioned these things, because I thought that it would be 
interesting to know, that audio compression algorithms may also act 
as noise gate filters. This does not need to be a bad thing. In most 
cases, this would be a very nice additional "feature".       



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