Theo Verelst Diary Page

Latest: Februari 9 2001

I've decided after good example to write some diary pages with toughts and events.

Oh, in case anybody fails to understand, I'd like to remind them that these pages are copyrighted, and that everything found here may not be redistributed in any other way then over this direct link without my prior consent. That includes family, christianity, and other cheats. The simple reason is that it may well be that some people have been ill informed because they've spread illegal 'copies' of my materials even with modifications. Apart from my moral judgement, that is illegal, and will be treated as such by me. Make as many references to these pages as you like, make hardcopies, but only of the whole page, including the html-references, and without changing a iota or tittel...

And if not? I won't hesitate to use legal means to correct wrong that may be done otherwise. And I am serious. I usually am. I'm not sure I could get 'attempt to grave emotional assault' out of it, but infrigement on copyright rules is serious enough. And Jesus called upon us to respect the authorities of state, so christians would of course never do such a thing. Lying, imagine that.

Previous Diary Entries

February 9, 2001

Looking around

I've been looking up a lot of things, for instance news on e-commerce laws in europe, though I could find no law texts or so straight away, just the article that made me think about the subject, intellectual property in general seems to be covered by 'wipo', though I think thats only advisory.

On the web programming side the methods to communicate between javascript on web pages and java applets are well examplyfied on this site, which may be good for future reference. I was looking at mathematical resources, and for instance found a truth table generator applet, fun stuff for in a course. The wavelad page is updated regularly, I'l dit down and do some good graphs on the applet to enhance understandability, one will have to wait for the software doing the wavs (provide a machine with windows 95+ or linux or so and they'll be there soon, in quite high quality form in no time) to listen to, though there are good enough examples. The theory and explanations are good, and not do readiliy available, not even book wise, as it will turn out.

I'll do some work making quite some effects and principles clear, that never hurts to make known how it is certain synths and soft should work good, and also isn't bad to be taken serious in the area at good level.

Looking at a way to make circuit structures visible on a web page, I found various 3D (the only valid model bases applets it seems are 3 and not 2D), I found a site with a lot of java 3D stuff listed, up to quite amazing quake kinds of interactive, textures images on a web page, remarkable (Frag Isaland).

I'l have a look at the models to see if custom models can be loaded, that's nice for example scenes. Some applets allow scenes to be loaded, but thus far I didn't find one controllable over javascript, which would be handiest. Pity tripods cgi's don't work too well, that would make at least changing models possible.

Commercial synthesizer development

The latest Yamaha, probably the main heavyweight source of new types of synthesis machines, synth module, 'phrase synthesis' based, I've looked up, and I found the user manual, which is good. I now know that it is a more interesting machine than I thought, it is a combination of the idea I thought it was, speach coding based signal generators, with an FM synthesis operator type of infrastructure. It in fact can read DX7 sounds and play them close to the original, and has two more operators, 8 instead of 6, has 8 types of basic waveforms, which is where it gets juicy, and two sets of 8 operators for each of its 32 voices of polyphony. I'm sure I'm at least on the right track in the r&d environment, because I started getting the ideas they probably base the machine on, and I like it.

Mainly, the generators with additional things such as envelopes and modulation called operators are no longer based on strict sine generators, as in the old dx synths, but generate partials of a (human) voice type of wave, which I think is a noise source with certain properties conceptually followed by a bandpass filter. The width of the bell-shape of the bandpass finter window can be adjusted, and the type of noise chosen from 8 kinds, for each operator. One set is only noise based, the other has oscilators. The combination of the noise source and bandfilter is of resonating nature, and in fact setting the bandwidth of the bandpass filter to 0 gives effectively a sine wave. Nice stuff, I didn't actively hear one yet, but 8 op FM with algorithms to liven and brighten up the sine ops is without question good for killer sounds, and a lot more than vocal sounds type of noises. The limitation is the number of partials, combined with their type of sound, which is natural, and a pleasant way of working in general, it makes for a characteristic yet rich sound module approach. There is a 'normal' multimode 4th order filter, too, so depending on the implementation of all this quite a sound spectrum should be possible.

This always depends on the type of signal processing and the parameter ranges, just like in many synths the sounds have their own character and limitation, for instance the DX7 and tx802 additive sounds are not as strong as when I make them myself with strict mathematics and not even so accurate DA conversion, for probably various reasons.

What's it with that vocal stuff? There are formants that make for the characteristics of a voice, that's the stuff used in certain speach coding algorithms, maybe on some wireless kinds. The main model is that the vocal tracts generate a sort of noisy tone, and the throath and mouth act as resonators and filters to shape that unarticulate noise in various ways, as physical filters, like a tube is filter, and of course by shaping the sound, for instance my simply opening or closing the mouth. The latter can produce lets say tone-less parts of speach, such as noise patterns for sses, p's etc, which is in the synth possible with the voiceless operators, and the main parts of lets say singing voices is a combination of noise generated by the volcal tract and passed trough, reverberating and resonating though every channel between the chest and the lips.

Having, without direct connection, done the noisy filter experiment lately, and checking the intrinsic human hearing wise strength of the sounds coming from it, the subject of using such type of generators is interesting. The idea in the vocal tract and resonating space is also as with the lips on a trumpet: the resonances determine the tracts' vibration, so the combination of the resonator and the oscilator is not a one way signal path from the generator though a filter, but the oscilator wave pattern and characteristics are influenced by the resonances going on.

Remebering the advancedness both soundwise and hardware wise of various Yamaha digital sound products, I'm not inclined to underestimate the amount of processing and the advancement of algorithmic thinking in the machine, which considering I only for a number of years realize how they probably did the fm voices (roughly) is more interesting.

The generator / bandfilter combinations can also be given a cross-feedback, I wonder wether that on top of the known fm-type of feedback makes use of this principle to have some of the effect I wanted (and at least started) to achieve in my waveguide simulator software.

I didn't hear this module yet, though of course it is possible I've hearded it in music or tune, and of course I know fm synthesis well. There are not that many real new synthesis algorithms around amoung a lot of sampling and known things, which is nice, and a major picture I;ve always had is that it takes research and development over a longer time at high level to do these things successfully. I recently looked up the 'gs 1' yamaha synth with organ type of cabinet, which I think is from even the late seventies, which has polyphony, and also fm synthesis elements I remember, indicating the advancement of the instrument at the time (though of course there were others, too) was a reason I justifiably had an interest at the time I heared about it. I think they used on at abba, leaving me guessing where, because I didn't have a list of instruments per song.

Link to yamaha's site, and an image

After all, this is not a .com site.

Electronics, system theory, digital circuits, and signals

Suppose I want to make a 20 bit analog to digital converter, at preferably 96 kHz or maybe 192 kilo samples per second, accurately, preferably with gain control from microphone levels to +4 dBm signal levels, an effective dynamic range of at least over a 100 dB (nice for multimedia type of applications with good audio systems), preferably some analog-related types of signal conditioning possible, and at least with a good spike, quantization, sampling and disturbance removing for digitizing from DA containing equipment.

And do it easy and cheap, preferably. The latter makes one go to a major (and maybe some minor) electronics companies, and check their latest chips in the area. Ti (Burr Brown), Analog, maybe national and some others have AD chips until at least 20 buts at audio rates, and better ones all the time.

I did reading in datasheets and some literature about balanced line driving, for long (e.g. adsl) lines but also for analog to digital converters. Midi and spdif probably not for nothing galvanically seperated interfaces by standard, yet many instruments are still connected up over normal lines, and mostly even unbalanced. Not that that is a problem, but the signal path to a analog to digital converter with a million quantisation steps would better be up to the job, and at least it makes sense to suppress disturbace though balancing.

The idea of using an existing chip is fine, and probably even affordable soon enough, but there are various aspects not covered by simply using such a device for every job in for instance mixers, or effect equipment, digital amplifiers and samplers/synthesizers.

The idea of using a digital conversion in the signal path makes sense enough for certain types of processing, though certainly not for all, so if sources are analog, it is not unwise to consider which parts of a design are going to be made digital (and back analog again) and what the point is of the digitisation. It is quite possible to add up to 6dB of anoying quantisation noise for each straight AD or DA pair in a signal path with certain amplification constants in between, which can be tens of dB for an output, a number of effect units, mixers, and mix processors on row.

And in terms of sampling and reconstruction distortion, there is a lot to be taken into account to be up to the 20 bit suggested quality.

There are fast ad converters of more limited accuracy around, as I mentioned, for instance 14 bit at up to over a hundred megaherz. It should be possible to use such one with a good sample and hold and/or filtering circuit and a fast enough DA converter and comparator circuit to digitize up until quite some bits at good enough rate, and if multiplexing signals can be made to work good enough, possible even for more than a few channels.

What does a O(50nS) output switcheable and .01% settling time 100 MHz opamp do in a switched signal path? If these types of parts work the way I think they can, including my cmos based DA converter up to signicant number of bits, then interesting circuits could be made. Pulse width controlled accurate amplifacation driving added, may make for a good signal path, without the need for fundamentally unpleasan noise shaping and dithering stuff.

Good part models (some of the sample datasheets have spice models !), and signal modeling would be good to do this type of design fundamentally right. Would HP realy have major theory in this area, doing up to 50 Gigaherz, 140 dB dyn. range, or would that just be long and many engineering hours? I'm sure what I picked up must be true that compuatation matters with some sufficient order of part models being theoretically connected up to maybe mathematically controlled accuracy transfer functions.

I guess I'd not be up to even the beginnning of such experience, although I'd at least qualify to start getting it, though my physics knowledge isn't to bad as an angle to such problems, I just currently don't find much possiblity to deal with such things. A highky fruitfull combination though, historically. And interesting also outside synthesis, although I think I like that subject.