Exeldrums

As I said in another blog post I find the computers of the 1980s French company Exelvision interesting and under-appreciated. Not only featured these computers (French) speech synthesis, but it had also one of the most interesting and quirky add-ons of the 80s: a digital drum computer (well, sort of)! Fitting into the naming scheme of Exelvisions products, it was called the “Exeldrums”. It was first sold in 1985 for 1200 French Francs (about 400 USD today).

Exeldrums: Complete product (without the manual)

Exelvision’s computer already came with a TI TMS5220 speech synthesis chip that was the same as in some of TI’s other products like the (last version of the) speech synthesis module for the TI-99/4A, the BBC Micro, and several arcade machines. It used something called “pitch-excited linear predictive coding (PE-LPC), where words are created by a lattice filter, selectably fed by either an excitation ROM (containing a glottal pulse waveform) or an LFSR (linear feedback shift register) noise generator. Linear predictive coding achieves a vast reduction in data volume needed to recreate intelligible speech data.” [Wikipedia]. The thing is that the Exelvision computers did not have a regular sound chip. In principle, you could use the speech synthesis chip also for sound effects, but it was a very complicated process to calculate the data for the synthesis chip given a target audio file. What Exelvision offered was to send them an audio cassette with the audio, then they would send this cassette to some TI labs in Dallas where a VAX computer would calculate the necessary data to feed the chip which you would get back as data on the cassette. As a result, even Exelvision’s own games have very sparse sound effects (and a lot of speech).

You could use a trick to generate some single channel audio, though. This trick consisted in using the cassette interface(!) and the timer to generate tones of a certain pitch and duration (see the last example in the section “Le composant audio” in [2] for an example).

So, all in all, the Exelvisions were not the best computers to do audio. Therefore, maybe in order to increase the attractivity of the machine to this market segment, two of the Exelvision engineers developed a cunning plan to use the computer as a drum machine (or at least a rhythm device). In true Exelvision fashion, an extension module was designed (all Exelvisions have an extension bay in the back), and some software written and put in a cartridge (they also had a cartridge slot in the front).

The module was designed around a rythm chip from Hohner (yes, the 150+ year-old German musical instruments manufacturer famed for their harmonicas). You see, Hohner used to manufacture a lot of different instruments in their day, and were in the 1960s and 1990 also famed for their range of innovative and popular electromechanical keyboard instruments. Between 1968 and 1976 they even produced (small) computers. In 1982 Hohner brought a successful series of home organs to market. Some of these models were sold in the US under the Wurlitzer brand, but stating on the case „Computer System by Hohner“.

This rhythm chip (the PCF0705) was manufactured by Philips. It is an interesting, but quite obscure chip. We know, of course, what it can do (see below), but apart from that we know basically nothing about it, not even a data sheet is available. This is because most probably, this chip was used only in Hohner products, and in Exeldrums…
All I found was a mention of this chip in a (Hohner designed) Wurlitzer “WX42 Keyboard Computer” because the seller mentions that you need to replace this chip if you want to get rid of the noise in the rhythm part of the keyboard…

Now, what can the Exeldrums do? Well, you can play 6 instruments in parallel out of a library of 17 drum and percussion sounds. These 17 instruments are clustered in 6 channels, and you can select one instrument per channel per time. The toms and the maracas are duplicated on two channels, so you can add them more often:

  • channel 0: bass drum, tom 1, tom 2
  • channel 1: hi-hat open, hi-hat closed
  • channel 2: cymbal, maracas
  • channel 3: snare drum, roll, brush, rim-shot
  • channel 4: maracas, tambourine, claves, tom 1, tom 2
  • channel 5: bell, hand clap

The resulting sound is probably good enough as a rhythm for a home organ, but it is no TR707: all sounds have the same length and the same volume.

The hardware module consists of the Hohner chip, a 32 kB ROM, a tiny (128 bytes) static RAM chip, and an analog/digital converter. You can hear the sound either via the TV or via the stereo cinch output at the back of the module.

Exelvision is a French company, producing computers mainly for France, and also the manual for the Exeldrums is in French. The software, however, has an English user interface 🙂

The basic screen is the classis TR707-style measure x sounds grid and you mark the beat where a sound shall be played. You can change the BPM, and you can have up to 57 sequences that can be saved onto tape or ExelMemory. In the software, you can use also one of 16 predefined rythms. Exeldrums can also be played from the Basic.

Here are all instruments (bass drum, tom 1, tom 2, hi-hat open, hi-hat closed, cymbal, maracas, snare, roll, brush, rim shot, tambourine, claves, bell, hand clap) played one after another each for 8 beats:

All instruments for 8 beats each, 50 bpm

There you have it: The Exeldrums digital “drum computer” module for the Exelvision family of computer in 1985. A rare and quirky add-on for a relatively rare French computer.

References

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