Z-DSP + + Z-DSP VC-DIGITAL SIGNAL PROCESSOR 2 4 B i t / Variable Clock Z-DSP L 1 VC-DSP1 IN 1 AUDIO IN 1 FEDBK IN MAX MIN MAX MIN VC-P1 MAX VC-DSP2 MIN 1 VC + FWD/REV VC-PRG MAX VC-P3 VC-P2 OUT1 VC-DSP3 MIN MAX CLOCK OUT2 ∑ MIN FEEDBACK 1 SEQUENTIAL PROGRAM CONTROL TRIGGER R T i p t o p Audio 2 2 IN 2 AUDIO IN MIN MAX MIN MAX FEEDBACK 2 2 FEDBK IN DSP FEDBK1 MIX FEDBK2 Tipt p DRY A u d i o User Manual Written By Mark Pulver Gur Milstein VC VC WET +
Z-DSP VC-Digital Signal Processor Design - Gur Milstein Special Thanks Alessandro Cortini Andreas Schneider Bobby Voso James Cigler Matthew Davidson Matrix Richard Devine Shawn Cleary Surachai Sutthisasanakul Special thanks to Mark Pulver for all the help and support in making this project a reality.
Contents.
Introduction. Welcome to the world of digital signal processing! The Z-DSP is a modular synthesizer component that can process and generate audio using a dedicated micro-computer, a digital signal processing processor – a DSP! Like the processor in your desktop computer, the Z-DSP runs programs in memory. It’s these programs that create the delays, filters, oscillators and more that the Z-DSP can produce.
Getting Started. The Z-DSP itself contains no programs, it loads programs from a cartridge. If the module is powered up without a cartridge inserted it will show “insert cartridge” on the display The module is sold with the Dragonfly Delay cartridge, which contains 8 delay programs. Pull it out of the bag now and insert it slowly to the card slot on the front of the Z-DSP, making sure that the Dragonfly print is facing upward.
Signal Flow. The Z-DSP contains two distinct audio channels, labeled Left (also “1”) and Right (also “2”). The terminology of “Left” and “Right” is most commonly used for stereo effects like Delay and Reverb, while “Channel 1” and “Channel 2” would be used in applications that deal with more diverse names such as Carrier and Signal in a ring modulator.
Analog Feedback. Feedback is the process of taking an output and applying it (“feeding” it) back into an input. This technique is widely used in audio for a variety of applications and is an especially strong tool in DSP allowing samples to be re-processed. The Z-DSP offers an open-loop-feedback architecture N S Ethe R TuserC has A R TtheR Ifreedom D G E to insert which meansI that other processing devices in the feedback loop. For example, analog filters, frequency shifters, other DSP processors, etc.
Digital Feedback. Some algorithms process feedback internally, in the digital domain. The texture of digital feedback is much different and brings a very different flavor than analog feedback. Combining analog and digital feedback will bring even more depth to a sound. You’ll know that a program is using digital feedback I N S E RonT theC display A R T R as I DaGparameter.
Reading the Panel. The Z-DSP front panel contains graphics and typography to help you understand the signal flow and to indicate the functions of the knobs and jacks.
A built-in Guitar Preamp. The Z-DSP contains a simple monophonic Guitar preamp that can be enabled by 2 jumpers at the back of the unit. The first jumper allows a choice between synth (line) level and guitar level. INSERT CARTRIDGE HD5 3 2 1 2&3 = synth level HD5 3 2 1 1&2 = guitar level The second jumper enables the preamp for both inputs, or just the Left input.
Looking into Voltage Control. The Z-DSP contain 2 types of Voltage Control (VC), one is the regular analog control such as the Feedback gain and VC over the Wet/Dry mix. These can be swept at any speed and well into the audio range. The circuit is designed such that with the knob at the center of its rotation, feeding a +/-2.5V signal will sweep the parameter from 0-100% for the Feedback gain, or 100% Dry to 100% Wet for the Wet/Dry mix. The other type of VC is digital.
Looking into Voltage Control. - Cont input accepts positive voltages from 0-5V though higher values are fine and will not damage the module. For some sonic chaos, try pulsing this input from an analog sequencer such as the Z8000 Matrix Sequencer/Programmer. More on this in the Program Switching section. Overall the Z-DSP inputs are well protected against excessive voltages on the inputs.
Understanding Clocking. Probably one of the most powerful features of the Z-DSP is the CLOCK input. Your computer works by having a processor (CPU) execute lines of program code step by step. The processor runs at a speed that is controlled by a very fast clock. Your PC is running so fast that working with the machine is continuous and smooth.
Understanding Clocking. - Continued As we’ve discussed, the Z-DSP has a built in DSP processor. Along with the processor is a pair of 24bit analog to digital convertors (“ADC”) on the inputs and a pair of 24bit digital to analog convertors (“DAC”) on the outputs. The ADC samples the analog audio signal into digital data, while the DAC takes the digital data and converts it back to analog form.
Understanding Clocking. - Continued To start, let’s use the square wave output from a Z3000 VCO. First set the PWM knob to its center position, then set the Frequency and Fine knobs to maximum. At this point the Z3000 is set well above the 20Khz range, which will be our new sampling rate. Now while the Z-DSP is processing a fairly bright sound, plug the Z3000 square wave into the Z-DSP CLOCK input.
Understanding Clocking. - Continued Anything is game for the CLOCK input… Modulate the pulse width of your new clock; set it to a narrow pulse so that the detector in the Z-DSP is “hanging on the edge”; try mixing the output of multiple VCOs to create a random clock. As well as going slower, there is also a whole new set of effects that stem from going faster. Feel free to go as wild as you wish with this, you will not harm the Z-DSP.
Program Switching. The Z-DSP cartridges can contain up to 8 programs, each program being a set of mathematical algorithms that manipulate digital data. As mentioned above, the ADC brings an analog signal into the digital domain by capturing it repeatedly thus creating a sample. The DSP allows for various operations to be applied to a sample.
Program Switching. - Continued input the direction will be reversed. To control program switching from an LFO or envelope generator, use the VC-PRG input. A 0-5V voltage swing on this input will switch the program under the same terms as the TRIGGER input. Note that switching time will vary from program to program. For example, switching to a delay effect takes longer than switching a filter effect.
That should be enough to get you started...
