Rossum Assimil8or - Multi-Timbral Phase Modulation Sampler

Multi-Timbral Phase Modulation Sampler

Designed to provide a powerful, flexible sampling engine for modular synthesis, the ASSIMIL8OR Multi-Timbral Phase Modulation Sampler module is the latest incarnation of Dave Rossum’s decades-long pioneering of affordable professional sampling technology.

ASSIMIL8OR provides eight independent channels of sampling with sound quality that can range from extremely hi-fi to low fi, all with extensive real-time CV control.

Key ASSIMIL8OR features include:

• Eight-channel multi-timbral operation. Each channel will be available from its own independent output as well as appearing in the stereo mix output.
• Superb 24-bit A/D and D/A conversion.
• Mono or stereo sampling. Channels can be configured as eight mono voices, four stereo voices, or any combination. (Well, any combination that adds up to eight).
• The ability to assign up to 8 samples to each channel and select between them in real time via CV.
• DC coupling through the signal path for sampling of control voltages.
• Unique timbral capabilities with the ability to phase modulate samples by external analog signals or by other samples (a first, we believe).
• Variable sample fidelity with independently selectable sample rate and bit depth.
• Real-time CV control of bit depth.
• Real-time CV control of aliasing (from virtually none to lots).
• Extensive sample manipulation and looping capabilities.
• Sample scrubbing under CV control.
• One-shot or gated sample playback with variable attack and release times.
• Gate/trigger inputs and CV inputs for each sample that can be assigned independently for each channel to virtually any sample parameter. Examples include:Pitch
  Level
  Bit Depth
  Phase Modulation
  Pan
  Scrub
  Sample Start
  Sample Length
  Loop Start
  Loop Length
  Release Time
• A front panel accessible SD card for sample and preset storage.
• And a lot more…

Assimil8or Specifications

SAMPLE MEMORY 

2,300 seconds at 48kHz mono, freely allocatable between the 8 channels

SAMPLE RATES

48kHZ, 96kHZ, 192kHZ

A/D & D/A

24 Bits

INTERNAL PROCESSING

32 Bits

LATENCY

100 microseconds at the Mix Outputs

180 microseconds at the Individual Outputs

INPUTS

Sample L/R

2x 3.5mm mono socket

100kΩ Input Impedance

Gate/Trigger 1-8 

8x 3.5mm mono socket

100kΩ Input Impedance

1.6V threshold

Control Voltage A 1-8

8x 3.5mm mono socket

100kΩ Input Impedance

96 kHz sample rate

Anti-alias filtered to 20kHz bandwidth

Control Voltage B&C 1-8

16x 3.5mm mono socket

100kΩ Input Impedance

48 kHz sample rate

No anti-alias filtering

OUTPUTS

Mix Outputs L/R

2x 3.5mm mono socket

1kΩ Impedance

Individual Outputs

8x 3.5mm mono socket

1kΩ Impedance

POWER REQUIREMENTS 

+/-12V via 16-pin, Doepfer-style connector

CURRENT DRAW

220mA +12V, 30mA -12V

DIMENSIONS

28HP (W); Panel to power connector (with connector plugged in) 25mm (D)

SUPPLIED ACCESSORIES

1x Micro SD card
1x 16-pin, Doepfer-style cable
4x M3 screws
4x M2.5 screws
4x Nylon washers
1x Quickstart Guide

Dave’s Introduction to Phase Modulation

Phase modulation is a new kind of audio cross-modulation for sampled sounds.  It can produce rich and varied timbres and textures, as well as wild distortions and grating noises.

The word “new” is probably not accurate.  Modular synthesizers have used frequency modulation (FM) since their inception.  Low frequency FM produces nice vibrato effects, and audio rate FM creates interesting timbres.  But exponential FM alters the perceived fundamental frequency of an oscillator; linear FM is required to alter the timbre while staying on pitch.

When we use FM, we call the source of the modulation the modulator, and the oscillator being modulated is called the carrier.

In the early 1970’s, John Chowning discovered using digital oscillators that linear FM through the zero point (so the carrier actually reversed its oscillation) produced very diverse and pleasing timbres.  Yamaha further developed this technology, but while Yamaha continued to call their implementation “FM”, they actually were using Phase Modulation.  Also worthy of note, Don Buchla heard Chowning say that you couldn’t do “through zero” FM with an analog circuit, so Don did just that with his Music Easel’s Complex Oscillator.

Let’s look at some oscilloscope photos to understand the difference.  If I frequency modulate a sine wave with another sine wave, the ‘scope shows us the effect on the waveform.  (The modulator is on the bottom in blue, the carrier in yellow on the top):

Now let’s use a pulse waveform to modulate a sawtooth wave carrier:

Here you can see that when the pulse is high, the sawtooth gets steep, when it’s low, the sawtooth slope is slight.

Now let’s use “through zero” modulation and turn up the gain of the modulator to show how the sawtooth slope now goes downward (backward) when the FM goes negative:

Now, a big problem with through zero linear FM is that as the pitch of the modulator goes up, it has less effect on the carrier’s timbre.  Here’s the same setup as above, but with the frequency of the modulating pulse wave increased by 1.5 octaves.   Note that the carrier waveform is getting to be pretty much an ordinary sawtooth.

The solution, as Yamaha discovered, was to instead of modulating the carrier’s frequency, have the modulating oscillator modulate its “phase.”  What this means is that the modulator is directly changing the location in the carrier’s waveform, rather than changing the rate that the carrier oscillates by moving along through its waveform.  Here’s what a sawtooth phase modulated by a pulse looks like.  When the pulse goes high, the carrier skips ahead to a higher point in the sawtooth ramp; when it goes low, it skips back to a lower point.

But now when we increase the modulator’s frequency, the carrier is still dramatically affected.  And we can see also in this waveform cases where the pulse has skipped backwards or forwards over the sawtooth’s edge, creating more large edges at this point.

We can modulate the sawtooth with a sine wave too.  Here, you can see how phase modulation maintains the character of each waveform, giving a new timbre with the characteristics of both the modulator and the unmodulated carrier:

As a final example, here’s the waveform that results when a sawtooth is modulated by a violin sample.  The frequency and sharp edges of the sawtooth are maintained, but the complex timbre of the violin is added:

When first planning Assimil8or, I thought phase modulation might be a neat feature.  I was really surprised to find almost nobody had taken advantage of phase modulated sampled sounds.  My first few experiments were really exciting, and I hope you have fun exploring this capability of Assimil8or.

Assimil8or QuickStart Guide (PDF)

Assimil8or Manual (PDF)