> Date: Thu, 19 Aug 1999 16:15:27 +0200
> From: Ralph Smeets <[EMAIL PROTECTED]>
> Subject: Re: MD: 24 bits/MD standard
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> [EMAIL PROTECTED] wrote:
>
>> of BS; meanwhile 24 bit in could just truncate at 20 or 18. (The second
>> thing I wonder is if these 24 bit converters are for real, since stand alone
>> 24 bit ADC units cost thousands of dollars, and the new Sony MDs with 24
>> start at under US$300. But that's a whole nuther issue.)
>
> What are the specs of those 24 bit converters that cost thousands of dollars?
An
> audio AD converter just needs to be 44.1 kHz. That's rather slow for a ADC.
Note
> that if you use 8 times oversampling at the front-end, your AD converter runs
on
> 44.1*8 Khz ie, 352kHz.
>
> I know a 200 Mhz 24 bit ADC costs loads of money but a ADC that doesn't even
run
> on 1Mhz? They are normally very very cheap.
>
> Cheers,
> Ralph -> Who's glad the ugly German is back!
Ralph-
Professional studio 24 bit A/Ds (and DACs) tend to have specs of 115-120 dB
Dynamic Range and S/N of >108dB. The reason they are so damn expensive is
because when you have that kind of dynamic range, you have to be very
careful about various physical limits of electric signals before you convert
them, i.e. the analog section, power supply etc. needs to be of the lowest
noise possible, which means premium parts. At 24 bits (even at 20) you
actually begin to run into the inherent thermal noise within resistors which
cannot be eliminated, and this is why the S/N ratio doesn't match the
Dynamic Range for higher bit rate converters (we can hear information
sitting well below the thermal noise level).
But aside from that, you seem to be confusing sampling rate with bit depth.
Faster processors can certainly up the sampling rate--just speed up the
clock; increasing the bit depth is all about good old analog electronics
design expertise and much more difficult/expensive.
-Alex
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