Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP Path: utzoo!linus!philabs!prls!amdimage!amdcad!decwrl!dec-rhea!dec-kirk!williams From: williams@kirk.DEC (John Williams 223-3402) Newsgroups: net.analog Subject: Synthesizer Recommendations Message-ID: <3613@decwrl.UUCP> Date: Wed, 14-Aug-85 10:37:59 EDT Article-I.D.: decwrl.3613 Posted: Wed Aug 14 10:37:59 1985 Date-Received: Mon, 19-Aug-85 06:48:27 EDT Sender: daemon@decwrl.UUCP Organization: Digital Equipment Corporation Lines: 47 To answer some of your questions: Companding DAC's are neither linear nor logrithmic. This makes computation a major pain in the neck. Companding DAC's have an exponent and a mantissa. A true logrithmic converter would be the ultimate choice for modulation techniques, whereas a linear DAC would be best if you wanted to add alot of waveforms together. The advantages of a companding DAC would not be significant inside a closed box, the major advantage being noise immunity, and hopefully you could control this fairly well inside the box. The best realistic S/N ratio you should ever want is 95 dB. This is the limit for the human ear. This works out to 18 bits. 12 bits will yield about 70 dB, which is probably good enough for alot of applications. You can use a notch filter to improve this by setting it at the sampling frequency. There is very little you can do about the lower harmonics that are generated by the quantization error. I would seriously look into MIDI. Any piece of equipment that is worth anything will have this interface, because: 1) It allows digital recording 2) It allows synchronized playback 3) It allows modularity of different components. 4) It's *REAL* cheap to impliment. Some Suggestions: 1) Set the sampling rate at something that fits nicely with the temperment. Most modern keyboards are set at equal temperament, which is a compromise of harmony for transposability. 2) Do some research on the MIDI standard and include it. 3) Use lookup tables for all your functions except the really simple ones. This will probably mean a rather large ROM. Reconstruction just doesn't cut it at those speeds unless you have a CRAY 1. 4) Play test it. Get some professional musicians to try it. Good Luck, John Williams