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ACO160EVK Audio‐to‐Synth System
Direct audio pitch to DCO
square/sawtooth/sine oscillator output
Low‐latency MIDI out with included
STM32F100C4 uC
1V/octave pitch CV output
Zero‐ripple envelope follower with
eight rate settings
Modulation CV input with +/‐2 octave
range in semitone resolution
Gate output with user‐configurable
threshold
25Hz‐5.2kHz frequency tracking range
Hard sync square wave oscillator from
10Hz‐10kHz generated by uC
Applications
Real‐time pitch‐to‐MIDI using virtually
any monophonic audio source
Audio‐controlled synthesizers
Pitch‐to‐CV converters
Pitch‐dependent audio processing
Harmonizers
Guitar and other instrument
effects/stompboxes
Description
The ACO160EVK Audio‐to‐Synth system is an
evaluation system for the ACO160 audio‐
controlled oscillator, an ultra‐low latency, low‐
power frequency‐tracking oscillator suitable for
audio‐controlled music synthesizer applications.
The ACO160 contains a fundamental frequency
detector based on dual switched‐capacitor peak
detectors with frequency‐dependent decay
time for ultra‐wide detection range, ultrasonic
analog oscillator and frequency tracking engine
that forces the analog oscillator to run at 8192
times the frequency of the incoming audio
signal detected at the input. This ultrasonic
analog oscillator is then divided back down to
1
Audio‐to‐Synth Evaluation System
audio range using programmable dividers that
are controlled by the harmony CV input and
which cover a +/‐2 octave range with semitone
precision over the entire range.
Additionally, the ACO160 features an integrated
switched‐capacitor envelope follower which
exhibits zero ripple, even for the lowest
frequency signals the chip can detect (down to
25Hz). An integrated gate generation
comparator has the envelope signal wired to its
positive input and allows the user to set the
voltage on the negative input. This voltage
functions as the gate threshold and generates a
rail‐to‐rail gate CV output.
The ACO160EVK additionally includes a
balanced preamp with combo XLR + ¼" jack
input with 0‐50dB gain, adjustable high‐pass
and low‐pass filters for improved frequency
detection (if needed) in front of the ACO160
chip, a VCA controlled either by the built‐in
envelope follower or by an external source, an
auxiliary mixer to mix another synth voice after
the VCA, and a STM32F100C4 micro‐controller
to convert the frequency, envelope and gate
information provided by the ACO160 chip into
MIDI commands to control digital synthesizers.
The ACO160EVK is meant to assist analog or
digital synth manufacturers with designing
products using its unique ACO technology and is
not intended to serve as a finished consumer
product.
Ordering Information
Part Number
Package
ACO160EVK
PCB
st
999 SW 1
Ave. #1617, Miami, FL 33130
ACO160EVK
Size
140mm x 120mm
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Summary of Contents for second sound ACO160EVK
- Page 1 ACO160EVK Audio‐to‐Synth Evaluation System ACO160EVK Audio‐to‐Synth System audio range using programmable dividers that Direct audio pitch to DCO are controlled by the harmony CV input and square/sawtooth/sine oscillator output which cover a +/‐2 octave range with semitone Low‐latency MIDI out with included precision over the entire range. STM32F100C4 uC 1V/octave pitch CV output Additionally, the ACO160 features an integrated Zero‐ripple envelope follower with switched‐capacitor envelope follower which eight rate settings exhibits zero ripple, even for the lowest Modulation CV input with +/‐2 octave frequency signals the chip can detect (down to range in semitone resolution 25Hz). An integrated gate generation Gate output with user‐configurable comparator has the envelope signal wired to its threshold positive input and allows the user to set the 25Hz‐5.2kHz frequency tracking range voltage on the negative input. This voltage Hard sync square wave oscillator from functions as the gate threshold and generates a 10Hz‐10kHz generated by uC rail‐to‐rail gate CV output. Applications ...
- Page 2 ACO160EVK Audio‐to‐Synth Evaluation System Block Diagram of ACO160EVK Audio‐to‐Synth Evaluation System ACO160EVK Inputs and Outputs Name Direction Description PSU Input Power 9v PSU input with positive sleeve (compatible with included PSU) Audio In Input Audio input from Neutrik XLR‐¼” combo jack Audio Thru Input/Output Unbalanced minijack audio input (LINE IN) and output (LINE OUT) after 0‐50dB gain preamp Harmony Input 1v/oct minijack harmony input modulates square/saw/sine frequencies over +/‐2 octave range on 12‐note equal‐tempered scale VCA In Input External minijack VCA input, if unpatched VCA is controlled by the envelope follower from the ACO160 chip Aux In Input Minijack auxiliary audio input can be mixed in after the VCA Mix Out Output Minijack output of the auxiliary audio mixer Main Out Output ¼” mono main output (equivalent to the aux mixer out followed by master volume control ...
- Page 3 ACO160EVK Audio‐to‐Synth Evaluation System ACO160EVK Controls Name Type Description Preamp Gain Knob Adjusts preamp gain from 0‐50dB. HPF Switch High‐pass filter corner frequency set to 16/80/160Hz. LPF Switch Low‐pass filter corner frequency set to 300/1.2k/5kHz. Gate Knob Tunes gate threshold from 0v to 3.3v. Threshold Env Rate 8‐Pos Adjusts the envelope decay rate to accommodate various instruments. Select Rotary Use fast rate (CCW) with fast‐decaying sources like bass guitar and Switch slower rate (CW) for sources with complex harmonic profile like violin. Wave Switch Selects square/saw/sine wave for processing by VCA. Pitch Freeze Switch By default, connects gate out to FTRACK input to enable frequency tracking. Can be momentarily held in opposing position to disable frequency tracking and freeze the current pitch. ...
- Page 4 ACO160EVK Audio‐to‐Synth Evaluation System Quick Start Guide to your ACO160EVK system Thank you for choosing to evaluate this ACO160EVK system! Here are some basic instructions to make the most out of your ACO160EVK board: Basic Setup 1) Apply power via the included 9v power supply unit (PSU). This unit can handle 100‐240VAC at its input so will work worldwide, possibly with only a adapter for your local electric socket required. 2) Connect any audio input via the Neutrik combo jack (XLR or ¼” balanced or unbalanced). 3) Play your audio source at a comfortable volume and adjust the preamp gain until the highest green LED lights up on the peaks. If the gain is too high, the preamp will clip and the fundamental frequency detection might not work. Note that the red overload LED does not light up no matter how large the signal at the preamp out! 4) Adjust the gate threshold so that the gate LED turns on when no audio is being played. With plucked string instruments like guitar it may take some tuning to get the gate to differentiate exactly when a note is being played from the low‐level transients that occur when you mute the strings. Try to set the gate high enough so that the LED remains on when those quiet transient events occur. 5) For almost all cases the HPF and LPF can be left in their default, “open” settings (HPF OFF and LPF at 5kHz). In some extreme cases changing these filtering settings can help, for example if you use a contact mic with a handheld instrument and want to filter out potential low‐frequency knocks or percussive effects. Listening to ACO Analog Outputs 6) Listen to the ACO output via the ¼” main output. To hear the dry + wet sound, connect a 1/8” patch cable between the “LINE OUT” and the “AUX IN” minijacks and adjust the AUX MIX knob to get the desired mix (fully CCW for dry, fully CW for wet). Adjust the master volume (“OUT LVL”) knob to get the desired level coming out of the EVK. 7) Select SIN/SAW/SQR waves via the 3‐way switch to hear the different ACO waveforms. 8) Adjust the ENV RATE SELECT rotary switch to optimize the frequency tracking for the audio source chosen. NOTE: This should be an 8‐position switch, but in this version of the EVK the assembly house installed a 4‐position switch by mistake. I modified the PCB so that every other rate setting is accessible from the fastest to the second slowest. Instruments with very fast attack/decay and low power in the harmonics (like guitar and bass guitar) should work well with fast envelope rate settings (CCW) whereas instruments with slower attack/decay and strong harmonics (like bowed strings) should work well with slow envelope rate settings (CW). Human voice should work well somewhere in the middle. 9) Adjust the “HARM” knob to hear the various pitch shift settings. Here it is especially useful to mix the dry and wet signals together so it’s easier to hear what harmony interval is tuned. Note that the ...
- Page 5 ACO160EVK Audio‐to‐Synth Evaluation System 10) Place the ACO Mode (S1) switch with the upper switch in the right position. You may have to reset the microcontroller via the reset pushbutton switch. Adjust the SYNC FREQ knob to hear the effects of hard sync with various sync frequencies. Hard sync on the sine wave is especially juicy! Place the upper ACO Mode switch back in the left position to enable MIDI output. Controlling External Synths Via CV/MIDI 11) Patch the PITCH, GATE and ENV signals out to an analog synth of your choice and enjoy “playing” that synth with the audio source of your choice! 12) Connect the MIDI output to the digital synth of your choice via a standard MIDI DIN5 cable and enjoy “playing” that synth with the audio source of your choice. ACO160EVK Calibration All functions in your ACO160EVK should be fully calibrated before shipment but here is a description of the calibration options: 1) DC offset at the ACO balanced input is controlled via the “OFFSET” trimpot. 2) Pitch CV 1v/oct calibration is controlled by the “PITCH CAL” and “PITCH OFFSET” trimpots. PITCH CAL is adjusted to tune the SLOPE of PITCH CV out to 1v/oct. PITCH OFFSET is tuned to set the absolute PITCH CV output as close to 50Hz = 1v as possible. Note that the PITCH OFFSET trimpot adjusts the level into a 3‐bit flash ADC which sets the pitch offset to one of eight discrete steps and can be tuned as follows if 50Hz = 1v is not desired: Fully CCW: PITCH CV – 210mV (50Hz = 0.79v, 100Hz = 1.79v) Next step CW: PITCH CV – 140mV (50Hz = 0.86v, 100Hz = 1.86v) Next step CW: PITCH CV – 70mV (50Hz = 0.93v, 100Hz = 1.93v) Next step CW: PITCH CV nominal (50Hz = 1v, 100Hz = 2v) Next step CW: PITCH CV + 70mV (50Hz = 1.07v, 100Hz = 2.07v) Next step CW: PITCH CV + 140mV (50Hz = 1.14v, 100Hz = 2.14v) Next step CW: PITCH CV + 210mV (50Hz = 1.21v, 100Hz = 2.21v) Fully CW: PITCH CV + 280mV (50Hz = 1.28v, 100Hz = 2.28v) 3) The HARM TUNE trimpot tunes the HARM IN CV input to 1v/oct. NOTE: This 1v/oct scale is accurate only when the HARM knob is tuned to the unison position. If the HARM knob is tuned differently the HARM IN CV scaling might differ from 1v/oct slightly. 4) CAL button. Pressing this button initiates a fast three‐point auto‐calibration procedure to tune the ACO160 to the appropriate MIDI notes. Turn off your audio source and turn the preamp and gate threshold knobs fully CCW to ensure calibration can be executed successfully. 5) Reset button. If you try to convert an especially challenging audio source to MIDI, it can result in ...
- Page 6 ACO160EVK Audio‐to‐Synth Evaluation System ACO160EVK Schematic – Page 1 6 999 SW 1 Ave. #1617, Miami, FL 33130 ...
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