Field Guide

The B500 Sampling Keyboard models a sampler from the mid ’80s, with 4-voice polyphony and multi-channel note memory. The audio engine and user interface are based on the Casio SK-1. Many DIY enthusiasts have taken advantage of the affordability of this synth and pioneered circuit modifications to manipulate ROM address and data outputs for a variety of otherworldly sounds; a practice that has since been coined circuit bending.

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Section Details

1 Volume

Increasing volume above 50% engages speaker distortion with Internal Speaker blend greater than zero.

2 Internal Speaker

Sets blend between Direct output and Internal Speaker emulation.

3 Operation Modes

• Normal mode is the default mode of operation, supporting 4-voice polyphony.

• Solo modes 1 and 2 each provide separate monophonic voices, supporting different tone selection.

• Chord mode splits the keyboard and engages 3 or 4 note diatonic chords from F3 to C5, with chord type specification from C#5 to C6. Refer to synth labeling for chord type per note which includes: major, minor, 7th, minor 7th, minor-major 7th, augmented, diminished, suspended 4th, augmented, 6th, minor 6th, and half-diminished chords. If no type is supplied, chords default to major.

All modes can be sequenced via note Memory, refer to Section 10 below for details.

4 Effects

• Vibrato engages subtle pitch bending after an initial delay.

• Portamento bends each note up or down to pitch depending on if an existing note is being held below or above the played note.

5 Circuit Bending

Tapping the Circuit Bending button opens a new window containing three sections corresponding to Analog, Digital, and Clock sections of the internally modeled circuit. A fixed set of bend points have been provided that can be dynamically connected or configured with a wide variety of results mimicking actual bends on a ROM-based synthesizer.

Note that inter-section connections are unidirectional with respect to the point of origin. If a bend connection is modified, wire color will change to reflect routing from the source to a new destination. This allows for independent control of analog-to-digital or digital-to-analog bends, with each direction providing a unique effect.

6 Envelope Select

Tapping the Envelope Select button highlights the currently selected volume envelope. Each accidental key on the main keyboard represents a different envelope. Envelopes are pre-programmed with each tone and can be modified and saved in a preset. The display bar above the keyboard contains visual representations of each envelope type.

7 Synthesized Tone

Tapping the Synthesized button selects the synthesized tone, which defaults to reference pitch.

Tapping the Synthesizing button opens the drawbar which overlays partial values above the specific subset of natural keys that control each partial. These keys can be tapped or dragged to change the level of each partial from values 0 to 15. Each partial is labeled based on traditional organ pipe lengths from 16′ to 1′.

Note that synthesized tones are internally generated and are not impacted by Circuit Bending.

8 Sampled Tones

What else is there to say? These sampled tones are classics, we hope you enjoy them!

Note that selecting a sampled tone loads a pre-programmed envelope, and re-selecting the same sampled tone will re-apply this envelope. Envelopes with sustain or longer decays than selected sample length will loop automatically.

9 Rhythm

Tapping the Rhythm button highlights the currently selected beat. The lower section of the drawbar shows each available beat for the specific subset of natural keys that apply. Changing the beat is instantaneous and can transition mid-measure during playback. Tapping Tempo buttons changes BPM by +/-10.

Tapping the Fill-In button plays a preset fill with custom duration based on the selected beat. Fills transition mid-measure and will play to the end of the current measure, or the next full measure when tapped within a 1-2 beat grace period at the end of the current measure.

10 Memory Sequencing

Tapping the Memory button opens a new window containing a score-based view for recording simple melodies. In Normal mode, melodies can contain four note harmony, in Multi-Channel mode (Solo 1/2, Chord), melodies are monophonic or fixed diatonic chords.

Melodies can be manually entered using Note Length and Insert Rest for composition. Melodies can also be recorded live which may provide a less accurate notation for the performance but will play back exactly. Delete removes the current or previous note based on cursor position. Clear erases the entire sequence on the selected staff.

When recording live, rhythm always plays back to provide a reference for the beat. During manual playback, Sync Rhythm can be enabled so that the beat starts during playback. Enabling Repeat sets a loop point at the end of the last measure with playable notes.

Note that after programming and/or recording a melody, the Lock icon above the title bar can be enabled to ensure further edits are disabled.

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Continuous Sampling

• Continuous sampling for realtime glitch effects
• Sample loop editing for time and pitch manipulation
• Single or multi-part sequencing for sample playback—combine with continuous sampling for additional chaos

Tapping the Continuous Sampling button engages a live sampling mode where the buffer used for playback is taken directly from stereo audio input. By default the buffer plays back at a normal rate, reproducing the original signal, slightly degraded by the limitations of the internal sampler. In addition to this, the keyboard or Memory sequencer can be used to trigger buffer playback at different sample rates. And in addition to that, Circuit Bending can be employed on sample buffer playback. With full stereo support.

Note that this mode is independent of the traditional internal mono sample buffer that can be used to capture and store samples for playback and manipulation.

11 Sampling

Tapping the Sampling button opens a new window containing an oscilloscope-style view for capturing samples and setting the loop point. Instructions to operate are as follows:

1. Drag the Threshold (horizontal line) up or down to establish a reasonable threshold slightly above the noise floor
2. If needed, adjust Gain and/or Range to set input level
3. Engage by tapping Record which transitions to an Armed state
4. Once the input signal exceeds the threshold an internal 1.4s buffer will fill with audio data
5. Drag the Loop Point (vertical line) left or right to establish where sample playback will stop and/or loop

By default, Left and Right inputs are summed to a mono, however Left or Right can be selected independently. Use Monitor to listen to sounds before and/or during recording. Dir/Mic sets blend between Direct input and Internal Microphone emulation.

By default, playback is normalized to A4, however Tune can be adjusted +/- 12 semitones to extend range or assist with tuning.

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Audio Unit Operation

• Section 9: Sync DAW Tempo

In addition to the specified controls above, a new button is made available when running SynthStamp as an audio unit. The Sync DAW Tempo button is provided which enables continuously tracking DAW BPM rates so that rhythms can be synchronized with DAW recording and playback.

The 5001 Analog Synthesizer models a dynamically patchable, semi-modular, monophonic analog synthesizer from the late ’70s. The audio engine and user interface are based on the ARP 2600. The front panel and extension panel on the keyboard present a majority of the controls and I/O from the original synth. The layout has been slightly modified for conciseness and to support stereo audio input. The drawbar in between the keyboard and the front panel can be dragged up or down to maximize either view for ease of use.

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Getting Started with Normalled Connections

If you’ve never worked with a synth like this before, or if you need a refresher, each control input is internally connected to an output as labeled on the synth without having to make any additional patches. Historically, this conserved patch cables for relatively frequent connections, allowing for more experimentation if cables were limited as well as kept the visual layout of a patch much simpler by avoiding unnecessary clutter. In a software incarnation with virtually unlimited patching normalling also serves as an effective starting point for learning the instrument. If you’re not sure how to begin or if you want to get to a usable sound fairly quickly, start by creating a new preset with no default patches, turn up some sliders, and start playing. Note that we’re using the term patch to refer to an individual connection between inputs and outputs as well as a generic term for the whole preset once all patches have been made, e.g. a patch can refer to either a single connection or the preset itself made up of multiple connections.

Key sliders to getting initial sounds include:

1. Section 8: Mixer Slider No. 2 (VCA)
   • Start here, enable output to speakers
2. Section 7: VCA Sliders No. 1 (VCF), and No. 3 (AR)
   • Next, enable output from VCF
   • Control volume with AR triggered by keyboard input
3. Section 6: VCF Sliders Nos. 1-3 (VCOs)
   • Route VCO square/saw outputs through VCF
   • Increase Initial Filter Freq. for brighter sounds

During step #3 you should begin to hear sound when playing the keyboard as you increase the VCO input levels to the VCF. Note that the keyboard input alters oscillator pitch, adjusts filter frequency, and triggers the volume envelope all at the same time! This simple patch produces a filtered combination of the three VCOs, tuned to the same pitch by default, without involving any patching. The sound is gated by playing the keyboard via the VCA and AR envelope generator. From here you can begin to alter tuning, modify filter cutoff for different timbres, and adjust envelope attack and decay for dynamics.

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Section Details

1 Stereo Preamplifier

Use the audio input selector in the app toolbar to choose Left and Right input channels: tap to assign L, double tap to assign R. Left and Right assignments can be the same channel for mono routing flexibility. With mono input buses, L/R automatically share the same channel.

2 Envelope Follower/Ring Modulator

The envelope follower generates a control voltage based on the amplitude of the supplied input signal. Note that the input is normalled to the sum of the Left and Right input channels (which is the same channel for mono input buses).

The ring modulator is a four quadrant multiplier producing the multiplication of two supplied inputs. Note that polarity is preserved such that phase can be inverted when supplying a negative input signal. The DC/AC switch inserts or removes DC blocking capacitors at each of the inputs. Select DC when multiplying control voltages, AC for strictly audio inputs.

3 Keyboard CV/Multiples

The keyboard control voltage (CV) is normalled to the VCOs and VCF, and is provided as an output here for additional routing.

The four multiples dynamically reconfigure based on their connections and can provide 1 input to 3 outputs, 2 summed inputs to 2 outputs, or 3 summed inputs to 1 output. Both voltage control and audio inputs are supported.

4 VCOs

The voltage-controlled oscillators (VCOs) have a range of 0.1 Hz – ~20 kHz, and 0.01 Hz – 30 Hz in low frequency (LF) mode. Frequency control has a range of +/- 2 octaves, fine tuning control has a range of +/- 1 semitone.

5 VCF

The voltage-controlled filter (VCF) has a range of 20 Hz – 20 kHz. Fine tuning control has a range of +/- 1 octave. Increasing resonance can cause self-oscillation near maximum.

6 Envelope Generators

There are two envelope generators producing either attack, decay, sustain, and release (ADSR) or attack, decay (AR) envelopes. They are normalled to the keyboard gate/trigger and have a manual control that can be tapped to trigger the envelope cycle. Additionally, an external source can be selected for gate/trigger which disables keyboard input. The keyboard gate/trigger are also made available here for external routing.

7 VCA

The voltage-controlled amplifier (VCA) supports two audio inputs and two control inputs. The initial gain can be used to “open” the VCA and set a default volume, applying additional control signals is additive.

8 Mixer/Reverb

The mixer section has several components related to system output. The Mixer sums two inputs to mono and provides a Mixer Pan control for the mono output. In addition to the mono output, the summed signal is routed to an internal Spring Reverb with separate Left and Right volume controls. Both the Mixer and Reverb outputs are made available for additional routing purposes.

In addition to the Mixer and Reverb outputs, a stereo Aux Input is provided as well as the full stereo System Output.

9 Internal Speakers

The Left and Right channels are routed through internal speaker emulations. Each channel can be separately blended between Direct and Speaker emulation outputs.

10 Noise Generator

The noise generator has two controls for spectrum (white, pink, etc.) and level, with one output. Increasing the spectrum control produces more high frequency energy by increasing the cutoff of the internal low pass filter.

11 Voltage Processors

There are four voltage processors. From the top, 1 and 2 are summed. The summed output and 3 have additional inverted outputs. And 4 is a lag processor, adding ramp and decay time to supplied control signal inputs. 1 and 3 are normalled to +10V which equates to the highest possible control voltage. 2 is normalled to Keyboard CV. And 4 is normalled to the Envelope Follower output.

Note that this section can be used to provide extra multiples if needed, as well as Keyboard CV inversion for interesting effects.

12 Sample & Hold/Switch

The Sample & Hold is driven by a clock signal provided internally or overridden by the External Clock input. The input, which is normalled to the Noise Generator output, is sampled based on the frequency of the clock signal and the sampled voltage is produced at the output. If supplied internally, clock speed is controlled by the second slider. Output level is controlled by the first slider.

The Switch is a bidirectional switch that reconfigures based on applied connections. The configuration can be either switching between A/B inputs to C [A | B >> C], or switching between A/B outputs from C [C >> A | B]. Switching is based on the same clock signal supplied to the Sample & Hold which can be overridden by the External Clock input.

13 Drawbar

The drawbar is provided for additional flexibility and can be used to resize the ratio between the front panel and the keyboard. This allows for more focus on patching or playing with smaller screen sizes.

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The Keyboard

• Highest-note priority
• Note memory
• Tuning options

The keyboard is automatically routed to the VCOs and VCF via KBD ON switches, as well as provided in Section 3 with KBD CV output, with the Gate and Trigger provided in Section 6. The keyboard produces a monophonic output with high note priority and note memory, i.e. highest note wins, after releasing the highest note, control voltage remains present at the output.

14 Keyboard Controls

Keyboard controls include toggling between Variable (0.5x-2.0x) and Fixed (~0.8x-~1.2x) interval tuning, as well as selectable Tuning (+/-12 semitones) and Portamento (0s-0.5s) controls.

Note that the Tone Interval controls (Variable, Fixed) adjust pitch spacing relative to Middle C (C4). Increasing these values spreads notes further apart, decreasing brings notes closer together, enabling crude microtonal tunings.

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Audio Unit Operation

• Section 3: DAW Clock Out

In addition to the specified controls above, a new output is made available when running SynthStamp as an audio unit. The DAW Clock output is provided in Section 3 which continuously tracks DAW BPM rates and re-syncs with measure playback so that rhythmic effects can be achieved in synchronization with DAW recording and playback.