Overview - Chapter 3

DSP. The DSP (Digital Signal Processor) chip inside the Q20 is what processes all signals in the digital domain and creates all of the effects (sometimes with the assistance of the microprocessor). The DSP chip has a limit to how many instructions (per sample) it can handle. Some effects take up a large number of instructions, while others take only a few. Generally, reverbs are big DSP hogs, while most other effects use relatively small numbers of instructions. When you route Òpatch cordsÓ between Blocks, each connection requires 1% of DSP power (2% if the level is not 0.0dB). If you run out of DSP power, the error message ÒDSP IS FULLÓ briefly appears. If this happens, consider substituting an effect that uses fewer instructions for one of the more DSP demanding effects you may be using.

Effect Memory. The on-board effect memory is primarily used for delay effects, but sometimes used by reverb effects (for pre-delay). In total you have 5.4559 seconds (or 5,455.9 ms), although the maximum delay time any single delay effect may have is 5 seconds. Once this memory has been allocated, the error message ÒEFFECT MEMORY IS FULLÓ will briefly appear when you try to apply more delay time to a delay effect than there is memory available. Note: If you have several delay Effect Blocks in a Program, they will share the total amount of effect memory that is available. If the total of all delay times equals that of available effect memory, you will not be able to increase any of the delay times until you decrease the delay time of one or more of the delay Blocks.

LFOs. The term LFO comes from the days of early synthesizers, where tremolo and vibrato effects were created using a Low Frequency Oscillator to modulate another oscillatorÕs pitch, or the filter or amplifier volume. In effect devices, LFOs are used to create effects such as flanging, chorus and Lezlie speaker emulation. The Q20 provides 4 LFOs per Program. Most pitch effects use 1 LFO, but some use 2. Also, some of the larger reverb effects use an LFO for a bigger sound. Example: If you try to add an effect using an LFO and you have already used all four LFOs in other Effect Blocks, the error message ÒOUT OF LFOsÓ briefly appears.

Microprocessor Assistance. Like most digital electronic music and audio products, the Q20 uses a microprocessor to run all basic functions like recalling, editing, comparing, storing, and renaming Programs, etc. However, some of the effect types use the microprocessor to assist the DSP chip in creating the effect, and the microprocessor is capable of assisting in this way for only one effect per Program. Three Pitch effects use the microprocessor: Phasor, Stereo Lezlie and Ring Modulator. Only one of these three may be used per Program. Example: If you try to create a Ring Modulator effect type when either a Phasor or Stereo Lezlie effect is already in use in the Program, the error message ÒBLOCK COMBINATION NOT ALLOWEDÓ briefly appears.

In the back of this manual, you will find an index of effect types, listing the percentage of DSP, Effect memory and number of LFOs required by each. Use this as a reference when one or more categories of limit handling have been exceeded and you wish to learn what options exist in reorganizing the Program.

Q20 Reference Manual

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