mcmahan@netcom.UUCP (Dave Mc Mahan) (11/26/90)
In a previous article, gt7865a@prism.gatech.EDU (COMER,MATTHEW BRIAN) writes: >Can anyone give me any practical advice on building my first DSP >project? I would like to build something that would sample at a rate >of at least 41KHz, 16 bits. I have some project building experience >and a pretty good electronics background. Directions to appropriate >literature would be apreciated, as well as any direct advice anyone >might have. I'd suggest doing a meticulous layout on a PC board if you want to use all 16 bits of accuracy. Crummy layout will always kill you with that type of resolution, as noise will creep in from EVERYWHERE! You might even want to try and put the A-to-D on a seperate board that is totally isolated from the rest of the board. By isolated, I mean the whole analog section, starting with a seperate transformer tap for the analog stuff, copper shield box that is soldered to the ground plane, and a liberal sprinkling of .1 ufd ceramic caps on every chip in the system. Noise will kill you if you really need all 16 bits. Just think, if you are sampling a 0 to 1 volt signal, the lsb represents only 15 microvolts. Also, stay away from switching power supplies if you can. Use analog regulators like the 7805, 7812, etc, with both large electrolytic caps and (once again) .1 ufd ceramic caps. Keep your leads to these caps as short as possible by soldering those puppies snug onto the PC board. The digital stuff you can wire-wrap, but do yourself a favor and make the PC-board for the A-to-D converter. If you don't have the resources, use copper clad vector board for the A-to-D section and get somebody with lots of low signal level analog layout experience to show you how to design the vector board and cut pads to maintain as much isolation as possible. Using vector board and then hacking up the groundplane is just a bad idea. In case you haven't figured it out yet, you should get paranoid about noise if you really want to use the full range of the A-to-D converter you have chosen. If you plan to have a D-to-A converter to create an output signal, use the previous tips for that section as well. As for the rest of your project, we might be able to help you more if we knew what you wanted to produce and the types of design tools (compilers, assemblers, and debuggers) you have available. >Comer, Matthew Brian >Georgia Institute of Technology, Atlanta Georgia, 30332 >uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt7865a >Internet: gt7865a@prism.gatech.edu -dave -- Dave McMahan mcmahan@netcom.uucp {apple,amdahl,claris}!netcom!mcmahan
ajb@iti.org (Al Boehnlein) (04/10/91)
I have an idea for a DSP project that might interest the guitar players out there. I was wondering if it would be possible to write a program that would produce tablature of a song. ajb
rona@videovax.tv.tek.com (Ronald K. Anderson) (04/12/91)
In article <ajb.671294655@hela.iti.org> ajb@iti.org (Al Boehnlein) writes: >I have an idea for a DSP project that might interest the guitar players out >there. I was wondering if it would be possible to write a program that >would produce tablature of a song. > > ajb Good luck! Unlike many musical instruments, the guitar often has 22 frets (half-step quantized pitches) and the distance between string pitches is only a 5th. This means that there is considerable ambiguity as to where in the tabulature you would place a note. e.g.: the following are ALL ways to finger the same C note: 3 5 7 10 12 15 17 19 22 |-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-| |0|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-| |-|-|-|-|0|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-| |-|-|-|-|-|-|-|-|-|0|-|-|-|-|-|-|-|-|-|-|-|-|-| |-|-|-|-|-|-|-|-|-|-|-|-|-|-|0|-|-|-|-|-|-|-|-| |-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|O|-|-| A good guitarist can hear the subtle changes in tone (spectral components) and can, with the help of the process of elimination (there can be no more than 6 simultaneous notes, and the order is usually obvious), can often determine a WORKING fingering. A computer program would have to be clever enough to know which fingerings are possible, which are not possible, which are probable, anatomically speaking. The task would be much easier if you had access to the guitarist, and could put a hex pickup on his guitar. This would eliminate the inherent ambiguity. This is a project that has long interested me, but my DSP experience is 0. My '81 college Sr. project was a monophonic real-time (analog) "harmonizer", and part of the problem was determining apparent pitch. Producing tabulature would have been merely an information display problem. But then there's the polyphonic nature of the guitar... -- Ron Anderson "He is no fool who loses what he cannot keep to rona@videovax.tv.Tek.com gain what he cannot lose." Jim Elliot, martyr
schriste@uceng.UC.EDU (Steven V. Christensen) (04/17/91)
On a related (well, sort of) note, regarding Electronic Guitar Tuning, that was precicely what our first Electronic Design project was this quarter. And let me tell you, that it is mucho difficult to quantify a vibrating guitar string without resorting to DSP technology (we were using strict analog). It was basically a mic, and amp, a filter to get rid of hi-freq garbage, and then the most futile attempt at a half-a-dozen methods to get a good signal to send to a freq-voltage converter (to determine if a string is in tune or not). Depending on 1) how the string was plucked, 2) where it was plucked, 3) how hard it was plucked, 4) how in-tune it already was, and 5) the phase of the moon, we got different results. Harmonics were popping in and out of the signal as the string amplitude diminished, and I can under- stand 1), 2) and 3) for this cause. Most surprizing was 4): Apparently there are natural harmonic resonating frequencies of the body of the guitar which heighten or dampen various harmonics. It also changed depending on how I dampened the vibration of the guitar with my body. All in all, a very frustrating project! Now to write up the report and explain why it didn't work 100%.... Steven Christensen Univ. of Cincinnati -- Steven V. Christensen U.C. College of Eng. schriste@uceng.uc.edu For the adventurous: svc@elf0.uucp
lance@motcsd.csd.mot.com (lance.norskog) (04/19/91)
schriste@uceng.UC.EDU (Steven V. Christensen) writes: >On a related (well, sort of) note, regarding Electronic Guitar Tuning, >that was precicely what our first Electronic Design project was this quarter. >And let me tell you, that it is mucho difficult to quantify a vibrating >guitar string without resorting to DSP technology (we were using strict >analog). > [ much frustration deleted ] According to the Hal Christiansen book (I've forgotten the title, but it's a huge book on computer music) you get much less harmonic junk if you put the pickup in the middle of the string. Pickups are down at the end particularly to get harmonics. And, of course, you want a separate pickup for each string. While we're on the subject of electronic musical instruments, are there any "lab i/o" MIDI boxes available? That is, you get a MIDI port, a DSP, and a bunch of A/D & D/A lines. You download programs via SYSEX and wire up your own stuff to the box. Lance Norskog of