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Envelopes in Follow Mode 

Using the 

PI

 in 

Follow

 mode allows the envelope to directly 

follow the amplitude variations of the input signal. The 

velocity of the input signal can be imparted onto the output 

envelopes. The envelope shape can be more complex than 

the sustain-decay envelope of 

Gen.

 mode. In 

Follow

 mode, 

the envelope and 

Gate 

outputs can fire at different times. 

Figures 3 

and

 4

 use a similar input signal as 

Figures 1

 and 

2

 in the previous section. Notice that the envelopes 

(represented by the blue waveform on the bottom) are not 

uniform. Also notice that the shape of the envelope 

correlates more strongly to the contours of the input source 

(represented by red waveform at the top) as opposed to 

the gate (represented by the orange waveform in the 

middle). The amplitude of the input source directly influences the envelope’s maximum 

voltage, allowing for more organic envelope shapes and 

introducing some variability into the CV output. 

In 

Follow 

mode the 

Decay 

knob controls how quickly the 

envelope decays when the input amplitude falls. The 

envelope attack is always very rapid. 

Figure 5

 illustrates 

the envelope shape when 

Decay

 is set fully 

counterclockwise

You’ll notice the envelope begins to 

resemble the input source more closely. This can be used 

as an audio output, as a frequency modulation source, or 

in other creative ways. 

In 

Follow

 mode, the 

PI

 envelopes are sensitive to the 

velocity of the input source and therefore produce a greater 

variety of envelope shapes. Because envelopes generated in 

Follow 

mode follow the 

amplitude of the input signal, louder sounds result in higher 

voltage envelopes, and quieter sounds result in lower 

voltage envelopes. 

Figure 6

 shows two waveforms: the 

envelope output in blue, and the input signal in red. The 

Decay

 knob is set very low in this example. The input 

signal consists of a bass drum hit followed by a high-hat 

hit. Notice the bass drum hit causes a relatively high 

voltage envelope, while the high hat produces a lower 

voltage envelope. See the Velocity Sensing

 

section

 

below 

for more information. 

Page   of 

9

16

Figure 3

Figure 4

Figure 5

Figure 6

Summary of Contents for Percussion Interface (PI)

Page 1: ... gain stage options a modular level audio output jack a 1 4 6 35mm input jack and envelope attenuation capabilities The PI Expander connects to the PI with an included ribbon cable and does not require a separate power header The two modules are only available together as a pair Percussion Interface and PI Expander features Sensitivity knob Low Medium High gain switch and clipping LED Sustain cont...

Page 2: ...cks PI Expander 5 Setting Input Gain 6 Using the PI with Various Sources 7 Envelopes in Gen Mode 8 Envelopes in Follow Mode 9 Velocity Sensing 10 Preventing Misfires and Undesired Gates 12 Calibrating Lockout Time for Gate Out 13 Sidechaining with the PI 14 Electrical and Mechanical Specifications 15 My Patch Notes 16 Page of 2 16 ...

Page 3: ...oriented towards the bottom of the module 3 On the back of the PI Expander you will see one 8 pin header Using the provided 8 pin ribbon cable plug one end of the cable to the PI Expander and the other end to the 8 pin header on the back of the Percussion Interface The red stripe on the cable should be orientated towards the bottom of both modules 4 Using the included screws securely attach the Pe...

Page 4: ...um pulse width is 5ms and the maximum is 0 5s Envelope Decay Knob The Env Decay knob sets the decay time of the envelope The envelope has an exponential curve Follow Gen Switch The Follow Gen switch selects between two envelope modes In Gen mode the envelope has a sharp attack followed by a sustain period and an exponential decay The attack and sustain period are synchronized with the gate output ...

Page 5: ...utputs an attenuated inverted envelope signal This jack functions like the Env Out jack located on the Percussion Interface module except that it can be attenuated with the Inv Level knob Audio Out Jack The Audio Out jack outputs an amplified version of the input signal It can be used as a pre amp for microphones or other low level signals to boost them to modular level The gain boost amount is de...

Page 6: ...ithout the PI Expander the gain range can be set using a jumper on the back of the Percussion Interface Note that if the jumper is missing completely the default setting will be MEDIUM GAIN Page of 6 16 L M H switch position Range Use Cases L Low Gain 0 2x gain Best for modular level and some professional line level signals M Medium Gain 0 20x gain Best for instrument line and some low impedance m...

Page 7: ...as possible The HIGH GAIN setting on the PI is typically the best setting for high impedance microphones Low Impedance Microphones Low impedance microphones such as professional vocal or drum microphones typically require setting your PI to MEDIUM GAIN In some situations LOW GAIN and HIGH GAIN settings will perform better so experiment to find the best setting Acoustic drums will often have a long...

Page 8: ...ger the PI In Gen mode it s easy to adjust Sensitivity until unwanted envelopes and gates are no longer generated Another use case for Gen mode is to trigger a PI with one part of a drum say the snare head but not with another part of the drum say the rim By setting the L M H switch and Sensitivity knob appropriately and placing the microphone in a location where it picks up the head louder than t...

Page 9: ...w mode the Decay knob controls how quickly the envelope decays when the input amplitude falls The envelope attack is always very rapid Figure 5 illustrates the envelope shape when Decay is set fully counterclockwise You ll notice the envelope begins to resemble the input source more closely This can be used as an audio output as a frequency modulation source or in other creative ways In Follow mod...

Page 10: ...in to respond to the dynamic range of a normal playing style A basic procedure for finding a good velocity sensitivity range is as follows 1 Flip the switch to Follow 2 Turn Sensitivity all the way up 3 While hitting the drum with maximum velocity turn Sensitivity down until the gate no longer triggers 4 Nudge Sensitivity up until the PI gate begins to fire again At this setting the Env Out and In...

Page 11: ...result in very little signal when the object is struct Attaching it more firmly or to a more firm section of the object can help in this situation Using a standard drum mic attached to a drum is a good way of introducing dynamics to your setup Drum mics are durable and typically easy to attach Clipping a microphone to the rim of a drum will enable you to use the rim as a trigger source more accura...

Page 12: ...second misfire we need to adjust the Sensitivity or Sustain Adjusting Sensitivity In Figure 12 we ve turned the Sensitivity knob down until only one pulse is generated This technique works best when using samplers drum machines or any source with repetitive sounds and consistent amplitudes Adjusting Sustain With input sources of variable or inconsistent amplitude such as an acoustic drum or a live...

Page 13: ...e the lock out period and prevent undesired gates This is similar to adjusting the Sustain knob in order to clean up drums with a long decay but the trim pot doesn t change the pulse width of the Gate output Setting the lock out period with the trim pot is useful in Gen mode as it enables you to adjust the Sustain pot freely to control the envelope shape without worrying about undesired triggers T...

Page 14: ...fires 6 Listen to the audio being ducked as you adjust Inv Level and Env Decay to set the amount of effect and recovery speed When triggered the Inv Out signal will jump low causing the VCA to drop the volume of the audio As the inverted envelope decays it rises back to its resting voltage and the audio source increases in volume The Inv Level knob controls the amount of decrease in the audio sign...

Page 15: ... 54dB 500x Clip light turns blue when signal post gain exceeds 2 5Vpp Gate is triggered when signal post gain exceeds 6 3Vpp Clip light flashes red when signal clips on Audio Out jack exceeds 10 8V Gate Out jack 1k output impedance 8V gate trigger signal 6ms 0 5s pulse width Env Out jack jack on PI main module 1k output impedance 9V peak sustain 60mV resting off 15ms attack time 70ms 6s exponentia...

Page 16: ...My Patch Notes Page of 16 16 Env Level Inv Level Env Out Inv Out Audio Out Input PI EXPANDER PERCUSSION INTERFACE IN Sensitivity Sustain Env Decay Follow Gen Gate Env Out ...

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