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1994-03-09
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Apparently-To: john.smith@gravis.com
GUS Programmer's Digest Tue, 8 Mar 94 17:06 PST Volume 9: Issue 24
Today's Topics:
GUS clipping
GUS Programmer's Digest V9 #23 (2 msgs)
simultaneous play & record
Standard Info:
- Meta-info about the GUS can be found at the end of the Digest.
- Before you ask a question, please READ THE FAQ.
----------------------------------------------------------------------
Date: Tue, 8 Mar 1994 00:39:32 -0500 (EST)
From: dionf@ere.umontreal.ca (Francois Dion)
Subject: GUS clipping
> From: "VISX80::GRECNER" <GRECNER%VISX80.decnet@musx53.zfe.siemens.de>
> Subject: clipping
>
> It would be very strange, if there's no such algoithm, in my opinion.
No, it's not strange. If there was, then it would be a feature called a
limiter, something that's not present on the GUS, since i can if i want
make it clip both in the digital and analog domain. However, if you cant
learn to mix properly on the GUS, you'd have the same problem on an analog
setup with a mixer. Even if you can get an analog limiter, it is a bad
thing to make it work continuously. The sound will be muddy and wont
have any dynamic range at all. Now, if you have a digital limiter, the
same problem will happen: no dynamic range and a muddy sound.
> And dangerous for the sound.
Digital clipping is no worse than analog clipping (that is, on a bipolar
amp... tube amp is a completely different story). Anybody who has used
a 12 bit sampler has had to deal with digital clipping when sampling drums,
and nobody complained about how bad it was and how there should be a
limiter circuit. And what about MOD files! Talk about MASSIVE digital
clipping! Still, there are some people who still listen to these...
> In this case, it's statistically really not so bad. But I still think
> it can't just clip the wave to the maximum voltage until the sum of
> all voices becomes less than the maximum...
Why not?? If you had 32 16 bit DACs connected to a mixer and drove all of
them peak to peak, you'd get clipping in analog. Either you add voltages
or values, the result is the same. In analog, you are limited to 2 volts,
in digital 16 bits. As simple as that. There is no way to avoid this
limit.
> The breaks all I was
> thinking about. But maybe I was wrong... If that's true, than it's
> really only me who can assign apropriate volume settings to all the
> instruments hoping the probability of not exceeding the maximum is
> great enough
Yes, you have to mix. It's not a question of hoping, it's a question of
not driving every sample at 127. At 100, you are at -6dB to give you an
idea...
> ... I don't like it, however. Aren't here any documents
> from Gravis describing this ? Or from Ensoniq as the GF1 is supposed
> to be a clone of some Ensoniq chip ?
Every single synths out there and anything that uses a mixer works like
that. You dont like it, well tough luck because you have a fixed limit,
in volts or bits, and it will always be like that.
> From: "Ford, Richard x2056" <rford@infocomp.csir.co.za>
> Subject: GUS+16-bit option or MAX?
>
> Morning all
>
> Please, can someone put me in the picture re the MAX? Should I go for the
> GUS and the 16-bit option now
Get it now. Look how long it took for the DB to show up... Unless you can
wait 3 months (roughly), you should get the plain GUS right now. The only
thing that the MAX will give you more than GUS+DB is a CDROM interface.
Ciao,
--
Francois Dion
'
IdMEDIA \ Managing: \ Publishing: \ Specialising:
CP 312 \ Equation de Base \ Cybernaute \ Multimedia & Telecom
St-Lambert, QC \ Francois Dion \ IDM Software \ design, publishing &
Canada, J4P 3P8 \ Fuzzy Logic \ Raving Up North \ testing(hard/software)
------------------------------
Date: Tue, 8 Mar 1994 12:11:40 -0700 (MST)
From: "Shawn T. Rutledge" <rutledge@enuxsa.eas.asu.edu>
Subject: Re: GUS Programmer's Digest V9 #23
> >> The GUS doesn't do anything like that. It simply sums the voices. Because
> >> of partial cancelling (some of the samples will be positive, while others
> >> will be negative), clipping rarely occurs when typical voice volumes are
> >> used.
>
> >Rarely? There is no algorithm to prevent it at all?
>
> It would be very strange, if there's no such algoithm, in my opinion.
> And dangerous for the sound. But I like the idea of signed approach
What do you mean by signed approach? That the 16-bit number represents
a signed integer rather than an unsigned one? I would think that would
be a necessity, not just a preference, as any AC waveform has both
positive and negative samples.
> to digital mixing. I didn't think of the data as being signed till now.
> In this case, it's statistically really not so bad. But I still think
> it can't just clip the wave to the maximum voltage until the sum of
> all voices becomes less than the maximum... The breaks all I was
> thinking about. But maybe I was wrong... If that's true, than it's
Not sure what you're talking about here either.
> really only me who can assign apropriate volume settings to all the
> instruments hoping the probability of not exceeding the maximum is
> great enough ... I don't like it, however. Aren't here any documents
I don't either. The idea of using 21-bit math and dividing down to
16 bits sounds better to me. Or using a DAC with greater than 16-bit
resolution...
>
> Nope. And from the usual sound quality of the GUS, there doesn't
> appear to be a need to systematically divide the sum to rigorously
> prevent the possibility of clipping, and the GUS would, in fact,
> sound worse had this approach been taken (since dividing by the number
> of voices, 32, would mean that only 11 bits of each voice would show
> up in the output).
I suspect that the reason it isn't a problem is that our current set of
samples has few if any full 16-bit peaks. The full dynamic range isn't
being used anyway; if it was, clipping would occasionally occur. Besides,
16 bits is supposed to give us something like 90 db of dynamic range,
right? So if an instrument is sampled in such a way that it uses only
11 bits, that is probably closer to its real-life dynamic range, and
we should think of the 16 bits as extra headroom for cases when instruments
pile up on top of each other and the amplitude is reinforced.
--
_______ KB7PWD
(_ | |_) shawn.rutledge@asu.edu
__) | | \__________________________________________________________________
* fusion * ham radio * IEEE * cyberspace * GUS * ARS * C * electronics *
------------------------------
Date: Wed, 9 Mar 1994 08:05:05 +1000 (EST)
From: s921880@minyos.xx.rmit.EDU.AU (Adam Craig Seychell)
Subject: Re: GUS Programmer's Digest V9 #23
If the GUS mixes the 32 voices simply by summing the samples ( digitaly )
then why is the Ultrasound limited to 20KHz sample rate when playing 32
voices. I first thought that it was because DAC might no beable to keep
up but now I know that mixing is done in the digital circuits, adding 32
samples at 44KHz should be a piece of cake.
This means the DRAM will have to transfer at a rate of 44100*2*32 bytes
per second. Which is fairly slow for 100ns DRAMs.
------------------------------
Date: Tue, 8 Mar 94 18:16:24 EST
From: Dan Liszewski <liszewsk@lf.hp.com>
Subject: simultaneous play & record
Forgive my ignorance but, I'm wondering if the GUS could support
simultaneous play and record. Is it possible, or is there something
about the card that won't allow it?
Thanks
Dan Liszewski
------------------------------
End of GUS Programmer's Digest V9 #24
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