[mad-user] 20 bit playback and DSP plugins

[Unorthodox Behaviour]

Greetings to Rob and the list!

I've been lurking for a while but now I'd like some
advice. For the lack of money for a 24/96 card, I just
bought a Hercules (ex Guillemot) Game Theatre XP 6.1
card, which features the Crystal CS4630 DSP with
18-bit ADC and 20-bit DAC. (It's the same chip as the
Videologic Sonic Fury, and the Turtle Beach Santacruz)

Using Mad I can listen to music when I set Mad's
resolution in both 24 and 32 bits, when the output
plugin is either wave out (Winamp critical update
installed). With the directx output plug, I get white
noise in both 24 and 32 bits.

Question 1 is: Is there a way to certify that the
resulting sound is taking advantage of the 20 bit
resolution of the card and that it's not just a
dithered to 16 bits sound ? (provided of course that
the card's drivers do actually support these 20 bits
of the ADC...)

Question 2 is: Does anybody know of any DSP music
enhancer Winamp plug that would support more than 16
bits ? The ones I tried did not work. I know some of
you have 24/96 cards and so I expect you might use DSP
plugins.

Thanks in advance for any tips!

By the way, and for your information, Terratec will
soon produce a new budget card, the DMX 6fire LT
priced below 150 euros. It's a full 5.1 channel 24/96
card (all channels being 5.1) with the same specs as
the existing 6fire but without the breakout box - a
definite best buy. Amazon.de and computeruniverse.com
already offer it as a preorder. Of course i'm not in
any way affiliated to these companies, it's just that
this will be my next card - cheaper than any 24/96
stereo channel card, even Terratec's.

Needless to say, since the time I left the list some
months ago, I have recommended Mad to some 100+ people
who use it daily. Moreover, Mad is used some 10 hours
per day on my PC... Long live MAD !

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[Ian Scott]

Post by Unorthodox Behaviour
Greetings to Rob and the list!
I've been lurking for a while but now I'd like some
advice. For the lack of money for a 24/96 card, I just
bought a Hercules (ex Guillemot) Game Theatre XP 6.1
card, which features the Crystal CS4630 DSP with
18-bit ADC and 20-bit DAC. (It's the same chip as the
Videologic Sonic Fury, and the Turtle Beach Santacruz)

...

Post by Unorthodox Behaviour
Question 1 is: Is there a way to certify that the
resulting sound is taking advantage of the 20 bit
resolution of the card and that it's not just a
dithered to 16 bits sound ? (provided of course that
the card's drivers do actually support these 20 bits
of the ADC...)

Unfortunately, if it's a 20-bit DAC and you feed it 24 bits of data, the
4 least signifigant bits just get chopped off which is not desirable. I
would venture to guess that 16 bits with MAD's dithering would be better
than 24 bits with the last 4 being ignored.

Ian

[Andre]

Post by Ian Scott
Unfortunately, if it's a 20-bit DAC and you feed it 24 bits of
data, the 4 least signifigant bits just get chopped off which is
not desirable. I would venture to guess that 16 bits with MAD's
dithering would be better than 24 bits with the last 4 being
ignored.

A slightly strange thing to venture....

Truncating 24bit data after 20 bits would give an effective 19.5
bits, _across the entire frequency range_.

Dithering is about generating a more accurate average value over a
range of samples. For example, alternating between two consecutive
16bit values would give an average half way between them i.e. 17bits
effective resolution, but only for signals upto 1/4 of the sampling
frequency.

To get an effective 20bit output from 16bit samples + dither, you
must limit your signals to 1/32 of the sampling frequency (ie 1.4 kHz
for 44.1 kHz sampling frequency).

The maths may be slightly more complex than I have made it out to be,
but I think the end result is the same: a true 19.5bit output is
likely to far superior to 16bit output + dither for almost all types
of music.

Andre
--






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[Unorthodox Behaviour]

Dear Ian,

Thanks for the fast reply !

My limited knowledge of digital electronics allows me
to venture that these 20 bits would be better than
even correctly dithered 16 bits, because I'll still
gain 4 more bits that were previously not accessible
with my old 16 bit hardware. In other words, I hope to
get 19 accurate bits, and a 20th bit that will be a
result of truncation and not dithering. As I see it,
this is an improvement over a properly dithered 16th
bit. But let's wait and see what the experts will say
:)

UB

Post by Ian Scott
Unfortunately, if it's a 20-bit DAC and you feed it
24 bits of data, the
4 least signifigant bits just get chopped off which
is not desirable. I
would venture to guess that 16 bits with MAD's
dithering would be better
than 24 bits with the last 4 being ignored.
Ian

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