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Subject: Re: 16/24bit?

Re: 16/24bit?

From: Rocker <rocker_at_shaw.ca>
Date: Wed, 13 Sep 2006 18:22:10 -0600

LOL!

I love the research dude!

I always thought that 2 inch tape is still the best!

rocker

----- Original Message -----
From: "Jerry Van Baren" <gerald.vanbaren_at_smiths-aerospace.com>
To: "Rockbox" <rockbox_at_cool.haxx.se>
Sent: Wednesday, September 13, 2006 7:46 AM
Subject: Re: 16/24bit?

David Pedersen wrote:
> Sorry, this migh be a silly question:
>
> I have approx. 200 MiniDiscs, filled with recordings. I now want to
> transfer them into my Archos. The miniDiscs are mainly recorded with
> 24bit technology. My soundCard on the computer only supports 16bit. Ok,
> I know, that it is no problem to record the 24bit discs with my 16bit
> soundcard, as I already have done so, in several cases; and then turn
> the whole thing into MP3. But my question is:
> Would I have any benefit of getting a 24bit soundcard for the
> computer? Does the MP3 technology care for 24bit? And will the RB/Archos
> give me better sound with the 24bits?
>
> David
> Archos JBR v1, RB2.5

 From an engineering point of view, 24 bits is entirely marketing hype
for everything but professional audio equipment, typically with very
high price tags (hundreds to thousands of dollars).

Dynamic range (dB) = 20 * log10(2^n)

Bits Signal range (dB)
16 96
17 102
18 108
19 114
20 120
21 126
22 132
23 138
24 144

In order to get 16 bits of useful resolution (i.e. 16 bits of signal) in
your digital stream, your analog front end (e.g. opamps plus associated
components such as resistors and capacitors) must have a combined noise
floor of significantly better than 96 dB.

You also need to look at the signal to noise quality of the A/D
itself... the highest quality A/Ds typically have a S/N rating of around
120-126 dB (21-21 bits). This means a very high quality A/D with a high
quality front end and an extremely high quality PCB (power supplies and
layout is incredibly important) gets you 20-21 bits of real signal plus
3-4 bits of noise. We are talking close to heroic measures with
proportional costs here.

The above is _before_ compression is applied.

So my answers to your questions are:

Q: Would I have any benefit of getting a 24bit soundcard for the computer?
A: No. Soundcards plugged into PCs don't have anywhere close to 24 bits
of useful resolution, despite the marking hype. PCI board physical
restrictions make proper board layout to achieve extremely high quality
audio impossible or nearly so. I suspect many, perhaps most, PC sound
cards struggle to achieve true 16 bits of signal to noise ratio. The
inside of a PC is saturated with electrical noise!

Q: Does the MP3 technology care for 24bit?
A: More bits is always better, but you will be throwing away a lot of
information in the lossy compression so the result is highly unlikely to
be distinguishable between "24 bits" and (true) 16 bits.

Q: And will the RB/Archos give me better sound with the 24bits?
A: Definitely not. The Archos hardware is nowhere close to the very
careful design that 16 requires and miles away from the heroic measures
that 20 bits require. The Archos was designed to be small, inexpensive,
and used in relatively high noise (not sound booth quality) environments.

I suspect, based on discussion on this mail list and my own empirical
listening experiences (but _not_ on actual measurements) that the Archos
hardware is probably on the order of 14 bits of signal and 2 bits of
noise. If you had a perfect 24 bit signal (say a computer generated
synth sound), you still cannot get any better than the Archos output S/N
(and that is ignoring the compression losses as well).

Minidisk audio is compressed as well (ATRAC), meaning your "24 bits"
isn't really.
   <http://en.wikipedia.org/wiki/Minidisk>

Are you sorry you asked now? ;-)
gvb
Received on 2006-09-14


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