This machine is big and heavy, much more so than the pictures you may have seen would indicate, around 4.5 kg or roughly 10 lbs. On the open market it will cost you from $800 from a broken one to $1500+ for a complete one with little use. This may seem outrageous for a drum machine of all things, and especially one which began production in 1983; however, you must take into account that the cream-colored steel box has magic in it, for real.
Connectors on the back include: MIDI in and out, save internal state to audio tape, foot pedal start/stop, DIN trigger in and out, all-instruments mix output, a proprietary data card slot, and individual outs for all instruments*.
It features an internal sequencer with 2 banks of 48 patterns, and 8 tracks which each can point to 896 patterns. This sequencer is fun to use today, and was stunning compared to its competition in the 80's, even compared to the rest of the Roland TR line. It allowed for step and individual voice pattern programming, and pattern programming could be done fast enough for live performance, as done in Richie Hawtin's contemporary Dex, Efex, and a 909 shows. The sequencer could be timed by DIN trigger sync and midi in, though it was notorious for drifting off time while a song was being played.
Because of its mostly analog internals, all twelve sounds could be played at once to create what have been termed "mad sick beatz". It would take affordable digital drum samplers another ten or fifteen years to achieve twelve-note polyphony, and some consumer-level boxes don't even have it in 2003. Also, nothing one can buy today has anywhere near the thirteen outputs on the back (12 instruments + 1 mixed), unless one wants to shell out a truly insane amount of money for a standalone sampler and a half dozen extra channel cards.
The sounds available on the machine, in their order across the control panel, are:
Accent: Also known as total accent, from the panel key used to program it. This allows you to set beats to have a global accent on all notes on that beat, making them a bit louder and in some cases subtly changing the character of the sound. Use this and the individual note accent (see below) together for even greater enfunkiment of chunkiness.
Bass Drum:* Aaah, this is perhaps the noise that the 909 is most famous for, and with good reason. Its sound has two parts, sine wave and noise, which are mixed together before amplification. The sine wave's frequency is controlled by the tone knob, and is generated by clipping a triangle wave, giving one factor of its unique sound. This wave is passed through an envelope generator with a knob-defined sharp attack, then a flat mesa top where a gradual peak would be expected, and a knob-defined slower decay. It is this envelope, which looks essentially like an extremely compressed bass drum, which really gives the BD its whomp after amplification. Noise is taken from the instrument's common noise generator, and is mixed in at a fairly low overall level -- still, it is this noise which is amplified or distorted to get an early 90's hardcore rave sound.
Snare Drum:* Unique among the drums on the 909 is the snare drum's composition, where the sound is made of both a resonating membrane and a set of snares that rattle against it. Because of this, there is an extra control knob marked "Snappy" which sets the amount of rattle (represented by a noise component) mixed into the final drum sound. Otherwise this is much like the BD above, with a sine component passed through sundry envelopes. The resulting sound is quite characteristic of the machine, and can be detuned, filtered, compressed, and otherwise fux0red to make all manners of sounds, few of them much like an actual snare drum.
Low, Mid, and High Tom: Three sine waves compose each of these, tuned differently for each voice's range. Rather than the 909's usual unnatural sine wave, one of the oscillators is even odder, as the clipper modulates from square to sine wave while the sound plays. This, along with the usual enveloped noise components, makes for a quite respectable analog tom tom sound.
Rim Shot: Instead of voltage control over this sound's oscillators, each of the three passes through its own band-pass filter. These are nominally set at 220, 500 and 1000 Hz, though they vary from machine to machine with the resistors and capacitors used. These are mixed is amplified as set on the control panel, and put through a final high-pass filter to get the high-pitched click of a rimshot. If you hear short ticks on every 16th note of a given techno track, this sound is one of the prime candidates for where it came from.
Hand Clap: Unlike most of the rest of the machine, this clap is functionally exactly like the clap on the Roland TR-808. It is composed of noise from the common noise generator, which is band-pass filtered, split, and sent through two envelopes. The first envelope has four separate attack stages, making it sound like a few people trying to clap at exactly the same time and nearly succeeding. The second envelope is much quieter and has a longer sustain, and gives the sort of hall reverb effect behind the clap. This sharp, hollow sound is another that the Roland boxes make in a way that simply nothing else does.
Open Hat, Closed Hat, Crash and Ride cymbals:* Last and freakiest of all of the voices are these, high-tech 18 kHz, 6-bit sampling from 1984. Now, already you may be thinking, "Six bits? That must sound like utter shit!" But check it out: Before sampling there wasn't any way to create an even remotely convincing cymbal sound with electronics. Talk all you want about filtering noise and putting it through a twelve stage envelope, in the end it always ended up sounding like something in-between a hiss and a fart ( take the Roland TR-606, for example). These 6-bit samples, though, changed everything -- you ended up with a noise that sounded at least something like an actual human whacking an actual cymbal, which with the right filtering could even sound warm and lively.
To do this with the technology available at the time, while still remaining remotely affordable, necessitated some fairly bizarre circuitry on Roland's part. Upon triggering any of these voices, a simple, non-crystal square wave oscillator begins pulsing at roughly 60 kHz, which is divided to get an approximation of the desired sample rate. The sample ROM pins out to a six-way flip-flop, making six output voltages possible; this is the entire DAC, possibly winning a prize for being the least complex ever. Samples were heavily compressed to have a higher resolution over their 6-bit range, so the signal must pass through an envelope that restores the original sample's dynamics. The signal then passes through an anti-log stage, making it louder overall, and passed through two low-pass filters to get rid of nasty high-end transients from the digital conversion. Tuning the crash and ride cymbals up or down requires sampling them at greater or lesser rates, and changing the envelope size to match.
Also, a couple of flexible rhythmic effects were built in, namely:
Shuffle:* This effect, when turned on for an entire pattern, added variation in the timing of the drum hits on beats two and four, theoretically giving the pattern's overall sound a more human feel. Realistically, this effect as implemented wouldn't sound remotely realistic in a rock song, but sounds plenty damn funky in hip-hop and Detroit techno -- another way Roland unintentionally created an electronic music monster. Can be set between 1 and 7, though 1 has no effect and 6 and 7 modify the beat to the point of silliness.
Flam: This could be turned used on the BD, SD, and all Toms. When turned on, it would trigger two hits each time a pattern indicated one hit, leading to possibly interesting rhythmic effects. Using a button on the control panel, it could be set to either be on or off for the entire pattern for each of the instruments listed. Also, there were seven possible settings for the duration between each drum hit, which did not vary timing with tempo.
Accent: Each note could be accented individually within the pattern, making its light brighter in pattern programming mode. Accenting a note changed slightly increased its volume and on some instruments subtly changed its character. This is almost like the velocity sensitivity that would come with later drum machines, though with only three stages (off, loud, and LOUD) it gave programs using it even more of a unique 909 feel.
* The star denotes special things (read: magic) the instrument is known for.