DIY eurorack modular synth Rasberry pi VCO with Seeed XIAO

This is a memorandum about HAGIWO/ハギヲ using seeed Xiao rp2040 and rasberry PI rp2040 to make your own VCO for the modular combiner.

background

53rd self-made modular synth.I took a poll on my Youtube channel and the Rasberry pi pico VCO was the most popular. However, the Rasberry pi pico has only 3-pin AD converter, and I was worried that it was a little inconvenient to use it as a VCO.

Under such circumstances, Seeed studio released a small microcomputer board called Seeed Xiao RP2040. Since the AD converter has 4 pins, I thought that I could make a VCO with a minimum configuration, so I planned this module.

product specs

Eurorack standard 3U 6HP sizepower supply: 45mA (at 5V) Canoperate with a single 5V power supply.

Digital VCO with 3 modes: Wavefold, FM and AM.Audio output uses PWM to reduce costs.Each mode has 8 built-in waveforms.

FREQ POT : Adjust frequency. Since it is for tuning, the adjustable frequency range is narrow.MOD POT : Adjust the amount of modulation applied.MODE SW: Toggle switch to switch modesOCT SW: Switch octave. Three ranges of -1, 0, +1.PUSH SW : Switch the tone. Eight tones can be selected in each mode.

MOD CV : Adjust the amount of modulation applied. The input range is 0-5V.V/oct : Control frequency. Input range is 0-5V, resolution is 10bit.OUT: Audio output, output range is 5Vp-p.

In Wavefold mode, it can also be used as a basic waveform VCO.In FM mode, you can get soft sounds and industrial waveforms with intense overtones.AM mode is intended for use with metallic percussion, and contains sounds that contain non-integer overtones.

Production cost

Total about 1100 yen---------------------------------Front panel 100 yenSeeed Xiao RP2040 600 yenToggle SW 20 yen *2pcsvariable resistor 30yen *2pcsoperational amplifier MPC6232 45yen etc.(see link below for general parts)

Seeed XIAO RP2040 is a microcomputer board equipped with the same RP2040 MCU as Rasberry pi pico. As for the number of AD converters, the pi pico has three, while the XIAO has four, making it easy to use.

hardware

Since the AD converter can read only up to 3.3V, the input range is expanded to 5V by dividing the voltage with resistors.The error of the voltage dividing resistance of the V/oct circuit is realized V/oct by performing software calibration.

Since the audio output is PWM, the output circuit has a 2-pole low-pass filter.It is amplified from 3.3Vp-p to 5Vp-p by an operational amplifier.Since it uses PWM, some harmonic noise is generated. If it bothers you, you should tune the low-pass filter.

2022/JUL/25 PostscriptThe toggle switch is an ON-OFF-ON 3-state switch.

NoteThere are multiple versions of the Seeed XIAO RP2040 schematic.The circuit diagram written as Ver1.08 is old and some circuits are different, so don't use it as a reference. Please refer to the circuit diagram written as the latest Ver1.22.

software

Notes on introducing Seeed XIAO RP2040

XIAO RP2040 can be developed with Arduino IDE.There is also a caveat here.When I installed the boards manager according to the software setup procedure on the official WIKI, writing failed in my environment.

XIAO RP2040 with Arduino - Seeed WikiSeed Product Documentwiki.seeedstudio.com

When I installed the board manager introduced by adafruit, I succeeded in writing.

Program RP2040 in ArduinoIn this guide, you'll learn how to install Earle Philhower'slearn.adafruit.com

It seems that other people have experienced similar problems, so if you fail to write with the Arduino IDE, you may want to suspect the board manager.

Baptism of XIAO RP2040 - ShigurememoIt's the consecutive holidays in May, and I thought I'd like to make something, so I bought the XIAO RP2040. I ordered it before the consecutive holidays and got it safely before the consecutive holidays. casuallymashigure.hateblo.jp

audio output

Waveforms are stored in a wavetable, interrupted at regular intervals, and the wavetable is read out to output audio. Wavetable is 10bit, 256 samples.In the August 2021 issue of the magazine Interfae, there was an article about a synthesizer using the Rasberry pi pico, and I used the source code as a reference. I could not understand 90% of what was written in my knowledge, but I was able to learn the concept of interrupt processing.

The source code is also available at the link below. Thanks!https://github.com/risgk/pico_synth_ex/blob/main/pico_synth_ex.c

You can also refer to this article. The concept of intervention is carefully explained.https://blog.boochow.com/article/pico-pwm-sound.html

Software calibration

There is a calibration constant to eliminate errors in the voltage divider resistance of the V/oct circuit.Calibrate by adjusting the value of calb in the range of about 0.7 to 1.3.

float calb = 1.19;//calibration for reduce resistance error

Advertise: Help Open Source Projects

In order to continue the open source project of DIY modular synth, we are looking for patrons on a service called patreon.I would appreciate it if you could help me with a cup of coffee.We also distribute content exclusive to patrons.

Source code

It's crude, but it's open to the public. If there is a bad point, I would be happy if you could point it out.

#include <hardware/pwm.h>

int k = 1;
float AM_mod = 1;//AM modulation rate
float f = 0;
int slice_num = 0;
float osc_freq = 0;
bool push_sw, old_push_sw;//push sw
float mod = 0;
int wavetable[256];//1024 resolution , 256 rate
float mod_wavetable[256];//1st modulated wavetable
int mod2_wavetable[256];//2nd modulated wavetable
float calb = 1.15;//calibration for reduce resistance error
int  adc, freq_pot, oct_sw, mode;
int waveform = 0;
int f0 = 35;//base osc frequency
long timer = 0;//use for making AM sinewave

const static float voctpow[1230] = {//Covers 6(=1230) octaves. If it is 1230 or more, the operation becomes unstable.
  0,  0.004882, 0.009765, 0.014648, 0.019531, 0.024414, 0.029296, 0.034179, 0.039062, 0.043945, 0.048828, 0.05371,  0.058593, 0.063476, 0.068359, 0.073242, 0.078125, 0.083007, 0.08789,  0.092773, 0.097656, 0.102539, 0.107421, 0.112304, 0.117187, 0.12207,  0.126953, 0.131835, 0.136718, 0.141601, 0.146484, 0.151367, 0.15625,  0.161132, 0.166015, 0.170898, 0.175781, 0.180664, 0.185546, 0.190429, 0.195312, 0.200195, 0.205078, 0.20996,  0.214843, 0.219726, 0.224609, 0.229492, 0.234375, 0.239257, 0.24414,  0.249023, 0.253906, 0.258789, 0.263671, 0.268554, 0.273437, 0.27832,  0.283203, 0.288085, 0.292968, 0.297851, 0.302734, 0.307617, 0.3125, 0.317382, 0.322265, 0.327148, 0.332031, 0.336914, 0.341796, 0.346679, 0.351562, 0.356445, 0.361328, 0.36621,  0.371093, 0.375976, 0.380859, 0.385742, 0.390625, 0.395507, 0.40039,  0.405273, 0.410156, 0.415039, 0.419921, 0.424804, 0.429687, 0.43457,  0.439453, 0.444335, 0.449218, 0.454101, 0.458984, 0.463867, 0.46875,  0.473632, 0.478515, 0.483398, 0.488281, 0.493164, 0.498046, 0.502929, 0.507812, 0.512695, 0.517578, 0.52246,  0.527343, 0.532226, 0.537109, 0.541992, 0.546875, 0.551757, 0.55664,  0.561523, 0.566406, 0.571289, 0.576171, 0.581054, 0.585937, 0.59082,  0.595703, 0.600585, 0.605468, 0.610351, 0.615234, 0.620117, 0.625,  0.629882, 0.634765, 0.639648, 0.644531, 0.649414, 0.654296, 0.659179, 0.664062, 0.668945, 0.673828, 0.67871,  0.683593, 0.688476, 0.693359, 0.698242, 0.703125, 0.708007, 0.71289,  0.717773, 0.722656, 0.727539, 0.732421, 0.737304, 0.742187, 0.74707,  0.751953, 0.756835, 0.761718, 0.766601, 0.771484, 0.776367, 0.78125,  0.786132, 0.791015, 0.795898, 0.800781, 0.805664, 0.810546, 0.815429, 0.820312, 0.825195, 0.830078, 0.83496,  0.839843, 0.844726, 0.849609, 0.854492, 0.859375, 0.864257, 0.86914,  0.874023, 0.878906, 0.883789, 0.888671, 0.893554, 0.898437, 0.90332,  0.908203, 0.913085, 0.917968, 0.922851, 0.927734, 0.932617, 0.9375, 0.942382, 0.947265, 0.952148, 0.957031, 0.961914, 0.966796, 0.971679, 0.976562, 0.981445, 0.986328, 0.99121,  0.996093, 1.000976, 1.005859, 1.010742, 1.015625, 1.020507, 1.02539,  1.030273, 1.035156, 1.040039, 1.044921, 1.049804, 1.054687, 1.05957,  1.064453, 1.069335, 1.074218, 1.079101, 1.083984, 1.088867, 1.09375,  1.098632, 1.103515, 1.108398, 1.113281, 1.118164, 1.123046, 1.127929, 1.132812, 1.137695, 1.142578, 1.14746,  1.152343, 1.157226, 1.162109, 1.166992, 1.171875, 1.176757, 1.18164,  1.186523, 1.191406, 1.196289, 1.201171, 1.206054, 1.210937, 1.21582,  1.220703, 1.225585, 1.230468, 1.235351, 1.240234, 1.245117, 1.25, 1.254882, 1.259765, 1.264648, 1.269531, 1.274414, 1.279296, 1.284179, 1.289062, 1.293945, 1.298828, 1.30371,  1.308593, 1.313476, 1.318359, 1.323242, 1.328125, 1.333007, 1.33789,  1.342773, 1.347656, 1.352539, 1.357421, 1.362304, 1.367187, 1.37207,  1.376953, 1.381835, 1.386718, 1.391601, 1.396484, 1.401367, 1.40625,  1.411132, 1.416015, 1.420898, 1.425781, 1.430664, 1.435546, 1.440429, 1.445312, 1.450195, 1.455078, 1.45996,  1.464843, 1.469726, 1.474609, 1.479492, 1.484375, 1.489257, 1.49414,  1.499023, 1.503906, 1.508789, 1.513671, 1.518554, 1.523437, 1.52832,  1.533203, 1.538085, 1.542968, 1.547851, 1.552734, 1.557617, 1.5625, 1.567382, 1.572265, 1.577148, 1.582031, 1.586914, 1.591796, 1.596679, 1.601562, 1.606445, 1.611328, 1.61621,  1.621093, 1.625976, 1.630859, 1.635742, 1.640625, 1.645507, 1.65039,  1.655273, 1.660156, 1.665039, 1.669921, 1.674804, 1.679687, 1.68457,  1.689453, 1.694335, 1.699218, 1.704101, 1.708984, 1.713867, 1.71875,  1.723632, 1.728515, 1.733398, 1.738281, 1.743164, 1.748046, 1.752929, 1.757812, 1.762695, 1.767578, 1.77246,  1.777343, 1.782226, 1.787109, 1.791992, 1.796875, 1.801757, 1.80664,  1.811523, 1.816406, 1.821289, 1.826171, 1.831054, 1.835937, 1.84082,  1.845703, 1.850585, 1.855468, 1.860351, 1.865234, 1.870117, 1.875,  1.879882, 1.884765, 1.889648, 1.894531, 1.899414, 1.904296, 1.909179, 1.914062, 1.918945, 1.923828, 1.92871,  1.933593, 1.938476, 1.943359, 1.948242, 1.953125, 1.958007, 1.96289,  1.967773, 1.972656, 1.977539, 1.982421, 1.987304, 1.992187, 1.99707,  2.001953, 2.006835, 2.011718, 2.016601, 2.021484, 2.026367, 2.03125,  2.036132, 2.041015, 2.045898, 2.050781, 2.055664, 2.060546, 2.065429, 2.070312, 2.075195, 2.080078, 2.08496,  2.089843, 2.094726, 2.099609, 2.104492, 2.109375, 2.114257, 2.11914,  2.124023, 2.128906, 2.133789, 2.138671, 2.143554, 2.148437, 2.15332,  2.158203, 2.163085, 2.167968, 2.172851, 2.177734, 2.182617, 2.1875, 2.192382, 2.197265, 2.202148, 2.207031, 2.211914, 2.216796, 2.221679, 2.226562, 2.231445, 2.236328, 2.24121,  2.246093, 2.250976, 2.255859, 2.260742, 2.265625, 2.270507, 2.27539,  2.280273, 2.285156, 2.290039, 2.294921, 2.299804, 2.304687, 2.30957,  2.314453, 2.319335, 2.324218, 2.329101, 2.333984, 2.338867, 2.34375,  2.348632, 2.353515, 2.358398, 2.363281, 2.368164, 2.373046, 2.377929, 2.382812, 2.387695, 2.392578, 2.39746,  2.402343, 2.407226, 2.412109, 2.416992, 2.421875, 2.426757, 2.43164,  2.436523, 2.441406, 2.446289, 2.451171, 2.456054, 2.460937, 2.46582,  2.470703, 2.475585, 2.480468, 2.485351, 2.490234, 2.495117, 2.5,  2.504882, 2.509765, 2.514648, 2.519531, 2.524414, 2.529296, 2.534179, 2.539062, 2.543945, 2.548828, 2.55371,  2.558593, 2.563476, 2.568359, 2.573242, 2.578125, 2.583007, 2.58789,  2.592773, 2.597656, 2.602539, 2.607421, 2.612304, 2.617187, 2.62207,  2.626953, 2.631835, 2.636718, 2.641601, 2.646484, 2.651367, 2.65625,  2.661132, 2.666015, 2.670898, 2.675781, 2.680664, 2.685546, 2.690429, 2.695312, 2.700195, 2.705078, 2.70996,  2.714843, 2.719726, 2.724609, 2.729492, 2.734375, 2.739257, 2.74414,  2.749023, 2.753906, 2.758789, 2.763671, 2.768554, 2.773437, 2.77832,  2.783203, 2.788085, 2.792968, 2.797851, 2.802734, 2.807617, 2.8125, 2.817382, 2.822265, 2.827148, 2.832031, 2.836914, 2.841796, 2.846679, 2.851562, 2.856445, 2.861328, 2.86621,  2.871093, 2.875976, 2.880859, 2.885742, 2.890625, 2.895507, 2.90039,  2.905273, 2.910156, 2.915039, 2.919921, 2.924804, 2.929687, 2.93457,  2.939453, 2.944335, 2.949218, 2.954101, 2.958984, 2.963867, 2.96875,  2.973632, 2.978515, 2.983398, 2.988281, 2.993164, 2.998046, 3.002929, 3.007812, 3.012695, 3.017578, 3.02246,  3.027343, 3.032226, 3.037109, 3.041992, 3.046875, 3.051757, 3.05664,  3.061523, 3.066406, 3.071289, 3.076171, 3.081054, 3.085937, 3.09082,  3.095703, 3.100585, 3.105468, 3.110351, 3.115234, 3.120117, 3.125,  3.129882, 3.134765, 3.139648, 3.144531, 3.149414, 3.154296, 3.159179, 3.164062, 3.168945, 3.173828, 3.17871,  3.183593, 3.188476, 3.193359, 3.198242, 3.203125, 3.208007, 3.21289,  3.217773, 3.222656, 3.227539, 3.232421, 3.237304, 3.242187, 3.24707,  3.251953, 3.256835, 3.261718, 3.266601, 3.271484, 3.276367, 3.28125,  3.286132, 3.291015, 3.295898, 3.300781, 3.305664, 3.310546, 3.315429, 3.320312, 3.325195, 3.330078, 3.33496,  3.339843, 3.344726, 3.349609, 3.354492, 3.359375, 3.364257, 3.36914,  3.374023, 3.378906, 3.383789, 3.388671, 3.393554, 3.398437, 3.40332,  3.408203, 3.413085, 3.417968, 3.422851, 3.427734, 3.432617, 3.4375, 3.442382, 3.447265, 3.452148, 3.457031, 3.461914, 3.466796, 3.471679, 3.476562, 3.481445, 3.486328, 3.49121,  3.496093, 3.500976, 3.505859, 3.510742, 3.515625, 3.520507, 3.52539,  3.530273, 3.535156, 3.540039, 3.544921, 3.549804, 3.554687, 3.55957,  3.564453, 3.569335, 3.574218, 3.579101, 3.583984, 3.588867, 3.59375,  3.598632, 3.603515, 3.608398, 3.613281, 3.618164, 3.623046, 3.627929, 3.632812, 3.637695, 3.642578, 3.64746,  3.652343, 3.657226, 3.662109, 3.666992, 3.671875, 3.676757, 3.68164,  3.686523, 3.691406, 3.696289, 3.701171, 3.706054, 3.710937, 3.71582,  3.720703, 3.725585, 3.730468, 3.735351, 3.740234, 3.745117, 3.75, 3.754882, 3.759765, 3.764648, 3.769531, 3.774414, 3.779296, 3.784179, 3.789062, 3.793945, 3.798828, 3.80371,  3.808593, 3.813476, 3.818359, 3.823242, 3.828125, 3.833007, 3.83789,  3.842773, 3.847656, 3.852539, 3.857421, 3.862304, 3.867187, 3.87207,  3.876953, 3.881835, 3.886718, 3.891601, 3.896484, 3.901367, 3.90625,  3.911132, 3.916015, 3.920898, 3.925781, 3.930664, 3.935546, 3.940429, 3.945312, 3.950195, 3.955078, 3.95996,  3.964843, 3.969726, 3.974609, 3.979492, 3.984375, 3.989257, 3.99414,  3.999023, 4.003906, 4.008789, 4.013671, 4.018554, 4.023437, 4.02832,  4.033203, 4.038085, 4.042968, 4.047851, 4.052734, 4.057617, 4.0625, 4.067382, 4.072265, 4.077148, 4.082031, 4.086914, 4.091796, 4.096679, 4.101562, 4.106445, 4.111328, 4.11621,  4.121093, 4.125976, 4.130859, 4.135742, 4.140625, 4.145507, 4.15039,  4.155273, 4.160156, 4.165039, 4.169921, 4.174804, 4.179687, 4.18457,  4.189453, 4.194335, 4.199218, 4.204101, 4.208984, 4.213867, 4.21875,  4.223632, 4.228515, 4.233398, 4.238281, 4.243164, 4.248046, 4.252929, 4.257812, 4.262695, 4.267578, 4.27246,  4.277343, 4.282226, 4.287109, 4.291992, 4.296875, 4.301757, 4.30664,  4.311523, 4.316406, 4.321289, 4.326171, 4.331054, 4.335937, 4.34082,  4.345703, 4.350585, 4.355468, 4.360351, 4.365234, 4.370117, 4.375,  4.379882, 4.384765, 4.389648, 4.394531, 4.399414, 4.404296, 4.409179, 4.414062, 4.418945, 4.423828, 4.42871,  4.433593, 4.438476, 4.443359, 4.448242, 4.453125, 4.458007, 4.46289,  4.467773, 4.472656, 4.477539, 4.482421, 4.487304, 4.492187, 4.49707,  4.501953, 4.506835, 4.511718, 4.516601, 4.521484, 4.526367, 4.53125,  4.536132, 4.541015, 4.545898, 4.550781, 4.555664, 4.560546, 4.565429, 4.570312, 4.575195, 4.580078, 4.58496,  4.589843, 4.594726, 4.599609, 4.604492, 4.609375, 4.614257, 4.61914,  4.624023, 4.628906, 4.633789, 4.638671, 4.643554, 4.648437, 4.65332,  4.658203, 4.663085, 4.667968, 4.672851, 4.677734, 4.682617, 4.6875, 4.692382, 4.697265, 4.702148, 4.707031, 4.711914, 4.716796, 4.721679, 4.726562, 4.731445, 4.736328, 4.74121,  4.746093, 4.750976, 4.755859, 4.760742, 4.765625, 4.770507, 4.77539,  4.780273, 4.785156, 4.790039, 4.794921, 4.799804, 4.804687, 4.80957,  4.814453, 4.819335, 4.824218, 4.829101, 4.833984, 4.838867, 4.84375,  4.848632, 4.853515, 4.858398, 4.863281, 4.868164, 4.873046, 4.877929, 4.882812, 4.887695, 4.892578, 4.89746,  4.902343, 4.907226, 4.912109, 4.916992, 4.921875, 4.926757, 4.93164,  4.936523, 4.941406, 4.946289, 4.951171, 4.956054, 4.960937, 4.96582,  4.970703, 4.975585, 4.980468, 4.985351, 4.990234, 4.995117, 5,  5.004882, 5.009765, 5.014648, 5.019531, 5.024414, 5.029296, 5.034179, 5.039062, 5.043945, 5.048828, 5.05371,  5.058593, 5.063476, 5.068359, 5.073242, 5.078125, 5.083007, 5.08789,  5.092773, 5.097656, 5.102539, 5.107421, 5.112304, 5.117187, 5.12207,  5.126953, 5.131835, 5.136718, 5.141601, 5.146484, 5.151367, 5.15625,  5.161132, 5.166015, 5.170898, 5.175781, 5.180664, 5.185546, 5.190429, 5.195312, 5.200195, 5.205078, 5.20996,  5.214843, 5.219726, 5.224609, 5.229492, 5.234375, 5.239257, 5.24414,  5.249023, 5.253906, 5.258789, 5.263671, 5.268554, 5.273437, 5.27832,  5.283203, 5.288085, 5.292968, 5.297851, 5.302734, 5.307617, 5.3125, 5.317382, 5.322265, 5.327148, 5.332031, 5.336914, 5.341796, 5.346679, 5.351562, 5.356445, 5.361328, 5.36621,  5.371093, 5.375976, 5.380859, 5.385742, 5.390625, 5.395507, 5.40039,  5.405273, 5.410156, 5.415039, 5.419921, 5.424804, 5.429687, 5.43457,  5.439453, 5.444335, 5.449218, 5.454101, 5.458984, 5.463867, 5.46875,  5.473632, 5.478515, 5.483398, 5.488281, 5.493164, 5.498046, 5.502929, 5.507812, 5.512695, 5.517578, 5.52246,  5.527343, 5.532226, 5.537109, 5.541992, 5.546875, 5.551757, 5.55664,  5.561523, 5.566406, 5.571289, 5.576171, 5.581054, 5.585937, 5.59082,  5.595703, 5.600585, 5.605468, 5.610351, 5.615234, 5.620117, 5.625,  5.629882, 5.634765, 5.639648, 5.644531, 5.649414, 5.654296, 5.659179, 5.664062, 5.668945, 5.673828, 5.67871,  5.683593, 5.688476, 5.693359, 5.698242, 5.703125, 5.708007, 5.71289,  5.717773, 5.722656, 5.727539, 5.732421, 5.737304, 5.742187, 5.74707,  5.751953, 5.756835, 5.761718, 5.766601, 5.771484, 5.776367, 5.78125,  5.786132, 5.791015, 5.795898, 5.800781, 5.805664, 5.810546, 5.815429, 5.820312, 5.825195, 5.830078, 5.83496,  5.839843, 5.844726, 5.849609, 5.854492, 5.859375, 5.864257, 5.86914,  5.874023, 5.878906, 5.883789, 5.888671, 5.893554, 5.898437, 5.90332,  5.908203, 5.913085, 5.917968, 5.922851, 5.927734, 5.932617, 5.9375, 5.942382, 5.947265, 5.952148, 5.957031, 5.961914, 5.966796, 5.971679, 5.976562, 5.981445, 5.986328, 5.99121,  5.996093, 6.000976,
};
float freq_table[2048];

void setup1() {
}

void setup()
{
  pinMode(0, INPUT_PULLUP);//oct select
  pinMode(1, INPUT_PULLUP);//oct select
  pinMode(6, INPUT_PULLUP);//push sw
  pinMode(3, INPUT_PULLUP);//mode select
  pinMode(4, INPUT_PULLUP);//mode select
  timer = micros();
  
  table_set();//set wavetable
  //-------------------octave select-------------------------------
  for (int i = 0; i < 1230; i++) {//Covers 6(=1230) octaves. If it is 1230 or more, the operation becomes unstable.
    freq_table[i] = f0 * pow(2, (voctpow[i]));
  }
  for (int i = 0; i < 2048 - 1230; i++) {
    freq_table[i + 1230] = 6;
  }

  //-------------------PWM setting-------------------------------
  gpio_set_function(2, GPIO_FUNC_PWM);// set GP2 function PWM
  slice_num = pwm_gpio_to_slice_num(2);// GP2 PWM slice

  pwm_clear_irq(slice_num);
  pwm_set_irq_enabled(slice_num, true);
  irq_set_exclusive_handler(PWM_IRQ_WRAP, on_pwm_wrap);
  irq_set_enabled(PWM_IRQ_WRAP, true);

  //set PWM frequency
  pwm_set_clkdiv(slice_num, 1);//=sysclock/((resolution+1)*frequency)
  pwm_set_wrap(slice_num, 1023);//resolutio
  pwm_set_enabled(slice_num, true);//PWM output enable


}

void  on_pwm_wrap() {
  pwm_clear_irq(slice_num);
  f = f + osc_freq;
  if (f > 255) {
    f = 0;
  }
  int k = (int)f;
  pwm_set_chan_level(slice_num, PWM_CHAN_A, mod2_wavetable[k] + 511);
}

void loop()
{
  old_push_sw = push_sw;

  //-------------------octave select-------------------------------
  if (digitalRead(0) == 1 && digitalRead(1) == 1) {
    oct_sw = 1;
  }
  else if (digitalRead(0) == 0 && digitalRead(1) == 1) {
    oct_sw = 3;
  }
  else if (digitalRead(0) == 1 && digitalRead(1) == 0) {
    oct_sw = 0;
  }

  //  -------------------mode select-------------------------------
  if (digitalRead(4) == 1 && digitalRead(3) == 1) {
    mode = 1;//fm
  }
  else if (digitalRead(4) == 0 && digitalRead(3) == 1) {
    mode = 0;//AM
  }
  else if (digitalRead(4) == 1 && digitalRead(3) == 0) {
    mode = 2;//wavefolder
  }

  //  -------------------frequeny calculation-------------------------------
  adc = analogRead(26) * calb;//Correct resistance errors
  adc = constrain(adc , 0, 1225) ;//Covers 6(=1220) octaves. If it is 1230 or more, the operation becomes unstable.
  freq_pot = map(analogRead(27), 0, 1023, 0, 127);
  osc_freq = freq_table[adc + freq_pot]; // V/oct apply
  osc_freq = 256 * osc_freq / 122070 * (1 + oct_sw);

  //  -------------------mod parameter set-------------------------------
  if (mode == 0) {//fold
    mod = constrain(analogRead(29) + analogRead(28), 0, 1023) * 0.0036 + 0.90; //28 is CV , 29 is pot
  }
  else if (mode == 1) {//FM
    mod = constrain(analogRead(29) + analogRead(28), 0, 1023) / 8;
  }
  else if (mode == 2) {//AM
    mod = 1023 - constrain(analogRead(29) + analogRead(28), 0, 1023) ;
  }

  //  -------------------push sw-------------------------------
  push_sw = digitalRead(6);
  if (push_sw == 0 && old_push_sw == 1) {//when push sw ON
    waveform++;//change waveform
    if (waveform > 7) {
      waveform = 0;
    }
    if (mode == 0 || mode == 2) {
      table_set();
    }
  }
//}

//void loop1() {//modulation
  if (mode == 0 ) {//wavefold
    for (int i = 0; i < 256; i++) {
      mod_wavetable[i] = wavetable[i] * mod;
    }
    for (int i = 0; i < 256; i++) {  //fold
      if (mod_wavetable[i] > 511 && mod_wavetable[i] < 1023 + 512) {
        mod2_wavetable[i] = 1024 - mod_wavetable[i];
      }
      else if (mod_wavetable[i] < -512 && mod_wavetable[i] > -1024 - 512) {
        mod2_wavetable[i] = -1023 - mod_wavetable[i];
      }
      else if (mod_wavetable[i] < -1024 - 511) {
        mod2_wavetable[i] = 2048 + mod_wavetable[i];
      }
      else if (mod_wavetable[i] > 1023 + 511) {
        mod2_wavetable[i] = -2047 + mod_wavetable[i];
      }
      else {
        mod2_wavetable[i] = mod_wavetable[i] ;
      }
    }
  }
  else if (mode == 1) {//FM
    switch  (waveform) {
      case 0:
        for (int i = 0; i < 256; i++) {  //FM1
          mod2_wavetable[i] = (sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 3 * i  / 256)) ) * 511;
        }
        break;

      case 1:
        for (int i = 0; i < 256; i++) {  //FM2
          mod2_wavetable[i] = (sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 3 * i  / 256 + mod / 128 * sin(2 * M_PI * 3 * i  / 256))) ) * 511;
        }
        break;

      case 2:
        for (int i = 0; i < 256; i++) {  //FM3
          mod2_wavetable[i] = (sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 5 * i  / 256 + mod / 128 * sin(2 * M_PI * 7 * i  / 256))) ) * 511;
        }
        break;

      case 3:
        for (int i = 0; i < 256; i++) {  //FM4
          mod2_wavetable[i] = (sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 9 * i  / 256 + mod / 128 * sin(2 * M_PI * 5 * i  / 256))) ) * 511;
        }
        break;

      case 4:
        for (int i = 0; i < 256; i++) {  //FM5
          mod2_wavetable[i] = ((sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 19 * i  / 256)) ) + (sin(2 * M_PI * 3 * i  / 256 + mod / 128 * sin(2 * M_PI * 7 * i  / 256)) )) / 2 * 511;
        }
        break;

      case 5:
        for (int i = 0; i < 256; i++) {  //FM6
          mod2_wavetable[i] = ((sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 7 * i  / 124)) ) + (sin(2 * M_PI * 9 * i  / 368 + mod / 128 * sin(2 * M_PI * 11 * i  / 256)) )) * 511;
        }
        break;

      case 6:
        for (int i = 0; i < 256; i++) {  //FM7
          mod2_wavetable[i] = ((sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 13 * i  / 256)) ) + (sin(2 * M_PI * 17 * i  / 111 + mod / 128 * sin(2 * M_PI * 19 * i  / 89)) )) * 511;
        }
        break;

      case 7:
        for (int i = 0; i < 256; i++) {  //FM8
          mod2_wavetable[i] = (sin(2 * M_PI * i  / 256 + mod / 128 * sin(2 * M_PI * 11 * i  / 124 + mod / 128 * sin(2 * M_PI * 7 * i  / 333 + mod / 128 * sin(2 * M_PI * 9 * i  / 56)))) )  * 511;
        }
        break;
    }
  }

  else if (mode == 2) {//AM
    if (timer + mod <= micros()) {
      k++;
      if (k > 63) {
        k = 0;
      }
      AM_mod = sin( 2 * M_PI * k  / 63);//make modulation sine wave
      for (int i = 0; i < 255 ; i++) {
        mod2_wavetable[i] = wavetable[i] * AM_mod;//multiply AM sine wave
      }
      timer = micros();
    }
  }

}

void table_set() {//make wavetable

  if (mode == 0) { //wavefold
    switch  (waveform) {
      case 0:
        for (int i = 0; i < 256; i++) {  //saw
          wavetable[i] = i * 4 - 512;
        }
        break;

      case 1:
        for (int i = 0; i < 256; i++) {  //sin
          wavetable[i] = (sin(2 * M_PI * i  / 256)) * 511;
        }
        break;

      case 2:
        for (int i = 0; i < 128; i++) {  //squ
          wavetable[i] = 511;
          wavetable[i + 128] = -511;
        }
        break;

      case 3:
        for (int i = 0; i < 128; i++) {  //tri
          wavetable[i] = i * 8 - 511;
          wavetable[i + 128] = 511 - i * 8;
        }
        break;

      case 4:
        for (int i = 0; i < 128; i++) {  //oct saw
          wavetable[i] = i * 4 - 512 + i * 2;
          wavetable[i + 128] = i * 2 - 256 + i * 4;
        }
        break;

      case 5:
        for (int i = 0; i < 256; i++) {  //FM1
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 3 * i  / 256)) ) * 511;
        }
        break;

      case 6:
        for (int i = 0; i < 256; i++) {  //FM2
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 7 * i  / 256))) * 511;
        }
        break;

      case 7:
        for (int i = 0; i < 256; i++) {  //FM3
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 4 * i  / 256 + sin(2 * M_PI * 11 * i  / 256)))) * 511;
        }
        break;
    }
  }
  else if (mode == 2) { //AM
    switch  (waveform) {
      case 0:
        for (int i = 0; i < 256; i++) {  //saw
          wavetable[i] = (sin(2 * M_PI * i  / 256)) * 511;
        }
        break;

      case 1:
        for (int i = 0; i < 256; i++) {  //fm1
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 3 * i  / 256)) ) * 511;
        }
        break;

      case 2:
        for (int i = 0; i < 256; i++) {  //fm2
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 5 * i  / 256)) ) * 511;
        }
        break;

      case 3:
        for (int i = 0; i < 256; i++) {  //fm3
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 4 * i  / 256 + sin(2 * M_PI * 11 * i  / 256)))) * 511;
        }
        break;

      case 4:
        for (int i = 0; i < 256; i++) {  //non-integer multiplets fm1
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 1.28 * i  / 256)) ) * 511;
        }
        break;

      case 5:
        for (int i = 0; i < 256; i++) {  //non-integer multiplets fm2
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 3.19 * i  / 256)) ) * 511;
        }
        break;

      case 6:
        for (int i = 0; i < 256; i++) {  //non-integer multiplets fm3
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 2.3 * i  / 256 + sin(2 * M_PI * 7.3 * i  / 256)))) * 511;
        }
        break;

      case 7:
        for (int i = 0; i < 256; i++) {  //non-integer multiplets fm3
          wavetable[i] = (sin(2 * M_PI * i  / 256 + sin(2 * M_PI * 6.3 * i  / 256 + sin(2 * M_PI * 11.3 * i  / 256)))) * 511;
        }
        break;
    }
  }
}

If you want to know more, this link can help you