Subject: Re: [linux-audio-dev] Linux support for IEEE1394 mLAN?
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Fri Sep 22 2000 - 02:36:17 EEST
about the floating - point ADC / DACs ...
is there, electronically speaking, a way to build them
so that they really always offer that kind of precison of the mantissa,
independently of the value of the exponent ?
how about non-linearity of certain electronic elements when dealing with higher
or lower voltages ?
But aren't standard high quality 24 bit DACs enough ?
Plus consider the fact the most DSP algorithms won't be able to retain a very
high precision, due to truncation, rounding and chaining errors.
In some cases you need all math done in 64bit fp (double precision), in order
to get the desired 16bits of precision at the DAC, using 32bit floating point
is not enough sometimes.
Plus some filters produce small ripples by definition, thus rendering the
added precision almost useless.
and at 24bit , we have some 144dB dynamic range which means quite
some headroom when recording.
Going above the 24bit audio is for me like trying to make movies with
200 frames per second ... no one will notice the difference, but
the cost and complexity of the system rises expotentially while not
giving us acceptable levels of improvement.
These are just my thoughts, but I may be wrong (and I'll happy to admit
it if someone points out what I'm missing).
Benno.
On Thu, 21 Sep 2000, Tom Pincince wrote:
>
> Something is definitely in the air. Just yesterday I was surfing 1394
> and ended up at yamaha's mLAN page. It seemed important at the time,
> and now this conversation confirms it.
>
> >Cool. How long can the cables be? And do you know a source
> >where I can look at cable pricing?
>
> I vaguely remember seeing 4.5 m as being the maximum, but I also saw a
> project that increased this to 70 m by converting to fiber optic. I did
> two searches through alta vista, one using 1394 linux and the other
> using 1394 audio, with the latter producing more interesting leads up
> front but I didn't bookmark anything.
>
> The thing that sparked my interest in this is that I am considering
> starting a project to design a multi-channel floating point a/d
> converter, and was contemplating the digital interface. I also read in
> Sound On Sound that Apple is releasing a fanless G4 (external power
> supply) with no pci slots at a discount price. Firewire and usb are the
> only ways to get into this box.
>
> Regarding the float a/d, I originally thought of it only in terms of
> potentially superior sound quality by making the input passive,
> providing impedance matching only and eliminating the need for mic
> preamps, and moving the amplification to the digital side of the s/h
> where the signal is dc and not reactive. I later realized that if I
> amplified the signal by a factor of 2 and did this multiple times until
> the signal became > = a reference voltage, that by counting the number
> of times the signal was amplified I would have the exponent of a
> normalized signal. This would give all signals, large and small, 24
> bits of precision. I remembered discussions here that referred to the
> desirability of float for dsp. If the a/d and d/a can be done in float
> then the entire digital domain can be float, if all one would wish to do
> digitally can be accomplished in float. Is this desirable? Please
> reply because your answers will weigh greatly in my decision to pursue
> this or not.
>
> Tom
>
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