Theo Verelst Local Diary Page 51

I've ditched the usual header for the moment, I think it doesn't help much anyhow.
This page is copyrighted by me, and may be read and transfered by any means only as a whole and including the references to me. I guess thats normal, the writer can chose that of course, maybe I´ll make some creative commons stuff one day, of course I have made Free and Open Source software and even hardware designs available!

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  Mon Aug 18 22:07, 2008


  Willy Nelson, need I say more

  same song, as was ´T´is weer voorbij die mooie zomer´ a big hit for Gerard Cox in Holland in early 70´s.

Lori Spee, one of the first CD´s I could try out on the first CD player in my room in the early 80s.

Parts and wholes



What a proposterous mess that is Theo!? Well, no I moved two computes where the server is a few meters, and ripped out all the cords not directly needed for the the webcam (Birdcam) and some basic audio facilities, so I pulled out Usb cables for xilinx boards, dsp boards, DA converter and photo cameras extra disc space, firewire connector for HD cam, various serial port cables for xilinx and DSP experiments, A xilinx programmer cable (parallel port) a Usb powered extension cord of 5 meter for wireless mouse charging or USB MIDI connection from a distance, Tos connector cables for the DA/AD converter, and I removed some scart and audio and video cables from the (normal) video digitizer box.

So you put all your cables and stuff on an impressive pile!? Oh no, the right picture shows yet another pile with Xlr microphone cable, jack cables, jack split and stereo to mono and balanced cables as well as long midi and optical cable

Less low level? A Xilinx Spartan 3 card with 1 megabyte fast static memory and periphierals and some IO and 120 pin connectors:

Can be connected up with this dual core Blackfin DSP board from Analog Devices

Pluck the night

I´m used to watching HD quite a bit

1920x1200 actual pixels and a Nvidia Quadro (pro) graphics card to drive them good.

<>The pluk de nacht film festival in Amsterdam:

Sines per second

Last page I observed gnuplot when called from  maxima gets certain graphs wrong so I made my own graph draw routine for use in my mathematical formula to soundwave web script.

now becomes this:

This image came up during testing:

See also the tcl wiki .

A very slow (low frequency) wave example:


Can you form the correct page url from the above information (the answer is here)?

In short, I could get about 10 million sine (in double format) computations per second from a PC. Funny in enough in 16 bits (a whole lot less) I get 10 times as many on a Spartan 3E FPGA, in practice! And with not so much troughput (pipeline) delay.

The formula synthesizer

It´s finaly reality: a Linux program driving sound via Jack, getting MIDI via Alsa which turns formulas/graphs like above into sound in realtime, without any messing with the waves.

I´ve use an example c program jackminisynth.c from the internet, and made sure it compiled, in this case on the server, a 64 bit Fedora 8 3.2GHz Athlon machine, which drives a Lexicon DA converter using Jack and Alsa or Oss, and which has a midi input as well, which can make it run under control of a midi keyboard. I had to update Alsa to get the development files ot install with Yum, and I recompiled Jack (version 103) because yum didn´t have the right version (anymore), which was annoying. After setting up the configure script and figuring out which libraries to use the sound C program works good.

<>Then I delved into the source a bit to find out how the sound samples were expected to be fed to the Jack calls, and made a prototype routine instead of the example which renders a formula like above directly into samples. In fact, I linked the program with the same Fortran routine created by Maxima so that the samples created on the page can also be in realtime created by pressing keys on the midi keyboard.

The advantage is that the samples can be controlled and made very accurately and for instance the sample can per correct design be almost (or completely) without aliasing errors when all frequencies in the formula are below the Niquist rate. Also the setup with jack and alsa connections (unlike plugins for instance) allows the program to be driven by sequencers and the output (in 2x32 bit floating point audio stream) can be recorded or processed by effects, in my case using Qjackctl.


Short example recording from a fairly random chosen wave from this program connected with ardour (mono track, 16 bits 44.1KS/s):

   math1.wav   (581 kilobyte)     math1.mp3 (53 kilobyte, 256 kbps)

I´ve coupled the sound generator, or in fact two different generators, one for melody and one for bass with a Rosegarden sequencer over MIDI from Alsa and recorded audio over Jack, and combined that with a drum sample (soundcanvas) and a DX7 simulation (hexter) for piano sound with some reverb, and all that on a notebook running Fedora 8, which also can compile the fortran into a working program, although I did get a problem with an incompatible library when trying a differential (not difference) equation solved symbolically and putting that into compiled fortran (some pow_4 instead of 8, appears to be fortran developpers fun to make backward incompatible libraries).

I used a hasta manana midi file from the internet and used 4 tracks, the result sounds purest in WAV file, but there´s a mpeg too

  h.wav   (3 min 10, CD quality stereo PCM 16 bit, 32 MegaByte)
 w.mp3   (3 min 10, 320 kilo bits per second mp3, 7.3 MegaByte download)

The left and right solo voice and bass are mathematical waves, IIRC from the example page.

Computer doom

Portable studio watts ?

It´s more atouch insane setup, but works great: One biamped monitor (with stereo bi-amping) driving as external biamped speaker a 15' neutrally boxed woofer and a small pioneer speaker as tweeter.

Normally the sub is driven by my previous main amp which is in 19 inch rack casing, with at least 100 Watts sine power per channel but considering it´s in bridge probably up to 300 or even 400 watts sine (!) power, which of course would be incredibly loud in a normal room. It is only driven with fairly well filtered frequencies under 40 Herz (most subs don´t even work well a bit above such frequency, but my main system has 12 inchers which dive well into the 30 herz range, and lower, themselves when needed) which sounds very soft at normal volumes (check the well known loudness sensitivy graph, easily ten times more power is needed for such low frequencies). And the max power is never reached, because even if I try some loud things out, there is currently a maximum in the signal chain, and I never put the end amplifiers that loud, ever. All for the better because the sub may handle a real 500Watts, it´s a big 15 inch, like in disco systems, and it is likely that if I´d adjust and solder the system a little different, it would actually have to handle such a music power, as I did demonstrate in public after I´d just built it.

Again luckily: the sub and to a lesser extend the main speakers and to yet a lesser extend the back (rear) speakers are damped. In the case of the sub, the back and sides are extremely damped:

Thats 3 (!) layers of heavy duty pro damping material back there!

Really, that much power ? Oh yeah, the main amp regulalry blew the automatic fuse when it was put on, so I had to make the currently limited startup circuit (albeit simple) which I described a few pages ago, and it has this superslow fuse, otherwise the fuse blows when the machine is put on on a heavy supply socket. TT means traag (traege) but extra, the superslow is conrad terminology, or possibly form the manufacturers datasheet. Well, I hear you compute, 3.15 amp times 230 Volts makes about 700 Watts, yeah, right. That is for four channels and the sub amp is a seperate machine. And the rear bi-amped (the front is triple-amped) system is seperately amplified and supplied, too.

I rearrange things often. Almost american-like lighting!

An Audi part!

Lets Fly

Not really. Well, there was a great sale at conrad for two model planes for under 30 Euro. And they really fly! But are foam models.

I did some flying hours with a more serious model: a chopper. But that has to have it´s 3d gear wheel change because the rotor hit the grass when I tried it out on such teritory. That´s a great model though, a fixed pitch multi digital channel electric machine of lets say 50cm which can do serious flying, as I test indoors, but in a small space, which isn´t nice.

A little movie from the tiny flying heli in mp4 format (straight from the Nokia Communicator).


What´s that?! A model helicopter, a pretty decent one, an electrical chopper with 2 servos and 2 motors and builtin gyroscope and cyclic pitchless flight control loop, leightwright frame with stif beam, ball bearings for the main rotor, and NiMh battery pack and multi channel transmitter of course. I did fly it years ago, and ´hopped´ and bit flown it recently but wouldn´t call myself sufficiently trained yet, but I got fairly good control when I concentrate. I don´t think it can lift an HD cam...