Date: Mon, 28 Oct 2002 11:03:39 -0600 (CST) From: Chris Dillon <cdillon@wolves.k12.mo.us> To: Dag-Erling Smorgrav <des@ofug.org> Cc: Soeren Schmidt <sos@spider.deepcore.dk>, Ronald G Minnich <rminnich@lanl.gov>, <"."@babolo.ru>, David Nicholas Kayal <davek@saturn5.com>, <freebsd-chat@FreeBSD.ORG> Subject: Re: Show me the light Message-ID: <20021028103905.T34529-100000@duey.wolves.k12.mo.us> In-Reply-To: <xzpwuo24jfj.fsf@flood.ping.uio.no>
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On Mon, 28 Oct 2002, Dag-Erling Smorgrav wrote: > Chris Dillon <cdillon@wolves.k12.mo.us> writes: > > Heh. Back when I had an 8086 XT and liked to listen to MODs and > > similar tracked music types, I built a very simple diode ladder DA > > converter that used the 8 output bits of the parallel port (9 > > output levels, so just slightly better than 3-bit resolution). > > Umm, if you do it right you get 8-bit (or 9-bit) mono. You're > limited to ~10 kHz though. I have one of these babies lying around > here somewhere; they were sold (ready-made and as kits) under the > brand name Covox. Sure, if you use a _real_ PCM DAC you can get 8-bit or better resolution out of it, but not when you're just using a diode ladder. The diode ladder cares not about the value of the binary data, only that as you turn on more of those outputs, the total output voltage goes up (8 outputs used, so 9 output levels possible, 0-8). In other words, it isn't PCM, but I don't know what you'd call it. Ideally, you would want to map the 256 possible 8-bit values to one of the possible 9 levels you would get out of the diode ladder and turn bits on accordingly. One of the MOD players I had did exactly that for those of us with diode ladders. One time I just fed the thing the raw audio and you could make it out, but it was really scratchy. It is obviously inaccurate when you feed it PCM except in the most extreme cases (i.e., all-zeros and all-ones values give you exactly what you want, nothing or everything), but anything in-between doesn't. If, for example, you have a value of 10000000, on a PCM DAC you would get exactly half of your maximum output, but with the diode-ladder, you only get 1/8'th. -- Chris Dillon - cdillon(at)wolves.k12.mo.us FreeBSD: The fastest and most stable server OS on the planet - Available for IA32 (Intel x86) and Alpha architectures - IA64, PowerPC, UltraSPARC, ARM, and S/390 under development - http://www.freebsd.org No trees were harmed in the composition of this message, although some electrons were mildly inconvenienced. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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