A Modular Approach to Audio Programming

https://mu.krj.st
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A comprehensive course and guide to low-level audio programming in C, exploring digital audio...
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### Install JACK and Example Tools

Source: https://mu.krj.st/notes/jack_freebsd.html

Installs the JACK audio connection kit and example tools using the FreeBSD package manager.

```bash
$ pkg install audio/jack audio/jack-example-tools

```

--------------------------------

### Start JACK server (OSS driver)

Source: https://mu.krj.st/notes/jack_freebsd.html

Starts the JACK audio server using the OSS driver. Recommended for basic setup.

```bash
$ jackd -r -doss

```

--------------------------------

### Install JACK and Dependencies on macOS

Source: https://mu.krj.st/notes/jack_macos.html

Installs the JACK audio server, qjackctl GUI, and pkg-config using Homebrew. Ensure Homebrew is installed first.

```bash
$ brew install jack qjackctl pkg-config

```

--------------------------------

### Install JACK on Arch-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs JACK2 and example tools on Arch-based systems. Ensure your user is added to the 'audio' and 'realtime' groups for proper functionality.

```bash
$ pacman -S jack2 jack-example-tools realtime-privileges

```

```bash
$ usermod -aG audio,realtime $USER

```

--------------------------------

### Command-line Execution Example

Source: https://mu.krj.st/ext

Example of how to run the LADSPA host from the command line, specifying the plugin file as an argument.

```bash
$ ./host ./sinosc.so

```

--------------------------------

### Configure Automatic Module Loading

Source: https://mu.krj.st/osc_i/joystick.txt

Example configuration for automatic module loading based on device types. Tailor these aliases and options to your specific hardware setup.

```bash
alias tty-ldisc-2 serport
alias char-major-13 input
above input joydev ns558 analog
options analog map=gamepad,none,2btn
```

--------------------------------

### Install QJackCtl

Source: https://mu.krj.st/notes/jack_freebsd.html

Installs QJackCtl, a graphical front-end for the JACK server, using the FreeBSD package manager.

```bash
$ pkg install qjackctl

```

--------------------------------

### Start JACK server with specific parameters

Source: https://mu.krj.st/notes/jack_freebsd.html

Starts the JACK server with specified sampling rate and buffer size using the OSS driver.

```bash
$ jackd -r -doss -r48000 -p1024

```

--------------------------------

### Install pkg-config

Source: https://mu.krj.st/notes/jack_freebsd.html

Installs the pkg-config utility, which is necessary for compiling JACK programs.

```bash
$ pkg install pkgconf

```

--------------------------------

### Example Device Output

Source: https://mu.krj.st/notes/pipewire_linux.html

Sample output from 'pw-cli list-objects Device', showing device details including 'device.name'.

```text
id 43, type PipeWire:Interface:Device/3
        object.serial = "45"
        factory.id = "14"
        client.id = "34"
        device.api = "alsa"
        device.description = "Built-in Audio"
        device.name = "alsa_card.pci-0000_00_1f.3"
        device.nick = "HDA Intel PCH"
        media.class = "Audio/Device"
id 77, type PipeWire:Interface:Device/3
        object.serial = "34705"
        factory.id = "14"
        client.id = "34"
        device.api = "alsa"
        device.description = "Focusrite Scarlett 2i2 2nd Gen"
        device.name = "alsa_card.usb-Focusrite_Scarlett_2i2_USB-00"
        device.nick = "Scarlett 2i2 USB"
        media.class = "Audio/Device"

```

--------------------------------

### Start Cadence

Source: https://mu.krj.st/notes/jack_linux.html

Launches the Cadence GUI application. Use this to configure JACK server settings.

```bash
$ cadence
```

--------------------------------

### Start JACK server with ALSA backend

Source: https://mu.krj.st/notes/jack_linux.html

Starts the JACK audio server using the ALSA backend. This is a basic command; parameters like sample rate and buffer size might need adjustment based on your hardware.

```bash
$ jackd -dalsa

```

--------------------------------

### Start JACK server with specific parameters

Source: https://mu.krj.st/notes/jack_linux.html

Starts the JACK audio server with specified sample rate (-r) and period size (-p). Adjust these values if the default settings fail.

```bash
$ jackd -dalsa -r48000 -p1024

```

--------------------------------

### Install PipeWire with JACK compatibility

Source: https://mu.krj.st/notes/pipewire_linux.html

Installs PipeWire, its JACK compatibility layer, wireplumber for session management, JACK example tools, and privileges for real-time operations. Run this command on Arch Linux.

```bash
$ pacman -S pipewire pipewire-jack wireplumber \
            jack-example-tools realtime-privileges

```

--------------------------------

### Install Cadence on Arch-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs Cadence and pulseaudio-jack on Arch-based systems. Ensure you have the necessary permissions.

```bash
$ pacman -S cadence pulseaudio-jack
```

--------------------------------

### Install QJackCtl on Arch-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs QJackCtl and pulseaudio-jack on Arch-based systems. These are required for manual JACK server configuration.

```bash
$ pacman -S qjackctl pulseaudio-jack
```

--------------------------------

### Install QJackCtl on Debian-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs QJackCtl and pulseaudio-module-jack on Debian-based systems. These are necessary for manual JACK server configuration.

```bash
$ apt install qjackctl pulseaudio-module-jack
```

--------------------------------

### Example PulseAudio Sink Output

Source: https://mu.krj.st/notes/pipewire_linux.html

This is an example output from `pactl list short sinks`, showing available audio output devices and their properties.

```text
54	alsa_output.pci-0000_00_1f.3.analog-stereo	PipeWire	s32le 2ch 48000Hz	SUSPENDED
34706	alsa_output.usb-Focusrite_Scarlett_2i2_USB-00.analog-stereo	PipeWire	s32le 2ch 48000Hz	SUSPENDED
```

--------------------------------

### Download sine.c example

Source: https://mu.krj.st/notes/jack_freebsd.html

Downloads the sine.c source file, a test program for JACK, using curl.

```bash
$ curl -OL https://mu.krj.st/files/sine.c

```

--------------------------------

### Install qpwgraph for PipeWire graph visualization

Source: https://mu.krj.st/notes/pipewire_linux.html

Installs qpwgraph, a graphical interface for PipeWire that supports PipeWire-specific features like video connections, useful for visualizing the audio graph.

```bash
$ pacman -S qpwgraph

```

--------------------------------

### Install JACK on Debian-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs JACK2 and development libraries on Debian-based systems. Add your user to the 'audio' group for necessary permissions.

```bash
$ apt install jackd2 libjack-jackd2-dev

```

```bash
$ usermod -aG audio $USER

```

--------------------------------

### Observe HTTP GET Request

Source: https://mu.krj.st/mix

This is an example of an HTTP GET request sent by a web browser to a server listening on localhost:80. It requests the root directory.

```http
GET / HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Upgrade-Insecure-Requests: 1


```

--------------------------------

### Example Node Name Output

Source: https://mu.krj.st/notes/pipewire_linux.html

Sample output from 'pw-cli list-objects Node | grep node.name', showing various node names.

```text
node.name = "alsa_output.pci-0000_00_1f.3.analog-stereo"
node.name = "alsa_input.pci-0000_00_1f.3.analog-stereo"
node.name = "alsa_input.usb-Focusrite_Scarlett_2i2_USB-00.HiFi__Mic1__source"
node.name = "alsa_input.usb-Focusrite_Scarlett_2i2_USB-00.HiFi__Mic1__source.split"
node.name = "alsa_input.usb-Focusrite_Scarlett_2i2_USB-00.HiFi__Mic2__source"
node.name = "alsa_input.usb-Focusrite_Scarlett_2i2_USB-00.HiFi__Mic2__source.split"
node.name = "alsa_output.usb-Focusrite_Scarlett_2i2_USB-00.HiFi__Line1__sink"
node.name = "alsa_input.hw_USB_0"

```

--------------------------------

### Example Ratio to Pole Calculation

Source: https://mu.krj.st/adsr

An example demonstrating the usage of the ratio2pole function with specific time and ratio values. The output represents the calculated pole.

```python
ratio2pole(1, 0.001/1.001)
```

--------------------------------

### Start JACK server with doas (root privileges)

Source: https://mu.krj.st/notes/jack_freebsd.html

Starts the JACK server with root privileges using 'doas' for improved real-time performance.

```bash
$ doas jackd -doss

```

--------------------------------

### Configure JACK Build

Source: https://mu.krj.st/notes/jack_win.html

Configure the JACK build process using the waf build system. Specify the installation prefix and check for GCC and G++ compilers. Ensure the prefix is set to MINGW_PREFIX for proper installation within the MinGW environment.

```bash
$ ./waf configure \
    --prefix=${MINGW_PREFIX} \
    --check-c-compiler=gcc \
    --check-cxx-compiler=g++
```

--------------------------------

### Initialize and Execute FFTW DFT

Source: https://mu.krj.st/spectrm

Initializes FFTW, populates input data, executes the DFT, and cleans up resources. Ensure FFTW is installed and linked.

```c
#include <fftw3.h>

#define N 16
static fftw_complex *in, *out;
static fftw_plan p;

void fftw_init(void)
{
  in = fftw_alloc_complex(N);
  out = fftw_alloc_complex(N);
  p = fftw_plan_dft_1d(N, in, out, 
                       FFTW_FORWARD, FFTW_ESTIMATE);
}

void fftw_finish(void)
{
  fftw_destroy_plan(p);
  fftw_free(in);
  fftw_free(out);
}

int main(void)
{
  fftw_init();

  // populate in
  fftw_execute(p);
  // use out

  fftw_finish();
  return 0;
}

```

--------------------------------

### Install JACK Dependencies on MSYS2

Source: https://mu.krj.st/notes/jack_win.html

Install essential dependencies for compiling JACK on MSYS2, including the MinGW-w64 toolchain, Python, and Git. Ensure these are installed before proceeding with JACK compilation.

```bash
$ pacman -S mingw-w64-x86_64-toolchain python git
```

--------------------------------

### Install JACK

Source: https://mu.krj.st/notes/jack_win.html

Install the compiled JACK components into the specified prefix. This command makes JACK available for use in your MSYS2/MinGW environment.

```bash
$ ./waf install
```

--------------------------------

### Complete FFTW DFT Example

Source: https://mu.krj.st/spectrm

A complete program demonstrating FFTW usage, including initialization, populating data, executing DFT, printing results, and cleanup.

```c
void fftw_init(void)
{
  in = fftw_alloc_complex(N);
  out = fftw_alloc_complex(N);
  p = fftw_plan_dft_1d(N, in, out, 
                       FFTW_FORWARD, FFTW_ESTIMATE);
}

void populate(void)
{
  size_t n;
  for (n = 0; n < N; ++n) {
    in[n][0] = n/(double)N;
    in[n][1] = 0;
  }
}

void print_result(void)
{
  size_t k;
  for (k = 0; k < N; ++k) {
    double re, im;
    re = out[k][0] / N; // <- normalization optional here
    im = out[k][1] / N;

    printf("%f\n", re*re + im*im);
  }
}

void fftw_finish(void)
{
  fftw_destroy_plan(p);
  fftw_free(in);
  fftw_free(out);
}

int main(void)
{
  fftw_init();

  populate();
  fftw_execute(p);
  print_result();

  fftw_finish();
  return 0;
}

```

--------------------------------

### Install Cadence on Debian-based systems

Source: https://mu.krj.st/notes/jack_linux.html

Installs Cadence and pulseaudio-jack on Debian-based systems. This involves adding a repository and updating package lists.

```bash
$ sudo apt-get install apt-transport-https gpgv
$ wget https://launchpad.net/~kxstudio-debian/+archive/kxstudio/+files/kxstudio-repos_10.0.3_all.deb
$ sudo dpkg -i kxstudio-repos_10.0.3_all.deb
$ apt update
$ apt install pulseaudio-module-jack cadence
```

--------------------------------

### Initialize liblo Server

Source: https://mu.krj.st/mix

Initializes the liblo server thread, sets up a handler for the /vol OSC message, and starts the server.

```c
static char *port = "10000";
static lo_server_thread st = NULL;

static void
lo_init(void)
{
  st = lo_server_thread_new(port, NULL);
  lo_server_thread_add_method(st, "/vol", "f",
                              on_message, NULL);
  lo_server_thread_start(st);
}
```

--------------------------------

### Start UDP Server with Netcat

Source: https://mu.krj.st/mix

Start a UDP server using netcat, listening on port 10000. This is used to receive OSC messages, which are typically sent over UDP.

```bash
$ nc -lup 10000
```

--------------------------------

### Cubic Scaling Example in Julia

Source: https://mu.krj.st/mix

This example demonstrates how to apply cubic scaling to a linear range and convert it to decibels. It uses a pipeline of functions to transform the data.

```julia
0:0.025:1 .|> (x -> x^3) .|> lin2db |> reverse .|> println;
```

--------------------------------

### Start TCP Server with Netcat

Source: https://mu.krj.st/mix

Use netcat to start a TCP server listening on port 80. This is useful for observing HTTP requests from a web browser. You might need sudo to bind to ports below 1024.

```bash
$ nc -lp 80
```

--------------------------------

### Control Rate Calculation Example

Source: https://mu.krj.st/ctrl

This example shows the calculation for control rate (kr) based on sampling rate (sr) and block size (nframes). It illustrates how to determine the frequency of parameter updates.

```plaintext
kr = sr / nframes

```

--------------------------------

### Compiling and Running Linear Interpolation Example

Source: https://mu.krj.st/denormal

Compiles and executes the C code that demonstrates potential numerical issues with floating-point linear interpolation.

```bash
$ gcc float5.c && ./a.out

```

--------------------------------

### Configure Spectrm Project

Source: https://mu.krj.st/assignments/spectrm_s.html

Run this command in the terminal to configure the spectrm project before compilation. Ensure all dependencies are installed.

```bash
./configure

```

--------------------------------

### Download Sine Wave Test File

Source: https://mu.krj.st/notes/jack_win.html

Download the 'sine.c' source file using curl. This C program is used to test the JACK installation by generating a sine wave audio output.

```bash
$ curl -OL https://mu.krj.st/files/sine.c
```

--------------------------------

### Switch JACK Server Master

Source: https://mu.krj.st/osc_i

This command-line example shows how to switch the JACK server's master clock using `jack_control`. This is an external command and not part of the C code.

```bash
$ jack_control sm
```

--------------------------------

### Start OSC server thread with liblo

Source: https://mu.krj.st/mix

Initialize a liblo server thread to listen on a specific port and register a handler for incoming OSC messages with a given address pattern and type tag.

```c
#include <lo/lo.h>

lo_server_thread st = lo_server_thread_new("10000", NULL);
lo_server_thread_add_method(st, "/vol", "f", handler, NULL);
lo_server_thread_start(st);

```

--------------------------------

### Display Local IP Addresses

Source: https://mu.krj.st/mix

Example output from the 'ip addr' command, showing various IP addresses including the loopback address (127.0.0.1) and a dynamic global IP address.

```text
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
inet 10.104.18.213/20 brd 10.105.31.255 scope global dynamic noprefixroute wlp2s0

```

--------------------------------

### Main Program Loop

Source: https://mu.krj.st/mix

Initializes liblo and JACK, waits for user input, then cleans up JACK and liblo.

```c
int main(void)
{
  lo_init();
  jack_init();

  /* idle main thread */
  getchar();

  jack_finish();
  lo_finish();
  return 0;
}
```

--------------------------------

### LADSPA Host Main Function

Source: https://mu.krj.st/ext

Initializes the LADSPA host by loading a plugin, initializing JACK, activating the client, and then idling. Ensure plugin path is provided as an argument.

```c
int main(int argc, char *argv[])
{
  if (argc < 2) {
    usage(argv[0]);
    return 1;
  }

  plugin_load(argv[1]);
  jack_init(descriptor->Label);
  ladspa_init();
  jack_activate(client);

  /* idle main thread */
  getchar();

  jack_finish();
  ladspa_finish();
  plugin_unload();
  return 0;
}
```

--------------------------------

### Initialize JACK Client

Source: https://mu.krj.st/osc_i

This function initializes a JACK client, retrieves the sample rate, registers a process callback, registers an output audio port, and activates the client. Ensure the JACK server is running or configured to start.

```c
static void
jack_init(void)
{
  /* 1. open jack client */
  client = jack_client_open("sine", JackNoStartServer, NULL);

  /* 2. get current sample rate */
  sr = jack_get_sample_rate(client);

  /* 3. register process callback */
  jack_set_process_callback(client, on_process, NULL);

  /* 4. register output audio port */
  port_out = jack_port_register(client, "out",
                                JACK_DEFAULT_AUDIO_TYPE,
                                JackPortIsOutput, 0);

  /* 5. activate our client */
  jack_activate(client);
}
```

--------------------------------

### Create a host program to load dynamic libraries

Source: https://mu.krj.st/ext

This C program uses `dlopen`, `dlsym`, and `dlclose` from `dlfcn.h` to load a dynamic library specified by a command-line argument, find and execute the `answer` function, and then unload the library.

```c
/* host.c: the host */
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

int answer(void);
typedef int (*answer_fn)(void);

int main(int argc, char *argv[])
{
  answer_fn f;
  void *handle;

  if (argc < 2)
    return 1;

  handle = dlopen(argv[1], RTLD_NOW);
  f = dlsym(handle, "answer");

  printf("%d\n", f());

  dlclose(handle);
  return 0;
}

```

--------------------------------

### Install LADSPA Plugin

Source: https://mu.krj.st/ext

Installs the compiled LADSPA plugin to the system's plugin directory. The exact path may vary depending on your Linux distribution.

```bash
$ install -m755 sinosc.so /usr/lib/ladspa
```

--------------------------------

### Initialize and Run Ring Buffer Test

Source: https://mu.krj.st/ctrl

Sets up a ring buffer and creates two threads for writing and reading. Ensure compilation with -O2 and -pthread.

```c
#define RB_SIZE 1024
static ringbuf *rb;

int main(void)
{
  pthread_t t1, t2;

  rb = rb_init(RB_SIZE);

  pthread_create(&t1, NULL, th_write, NULL);
  pthread_create(&t2, NULL, th_read, NULL);

  pthread_join(t1, NULL);
  pthread_join(t2, NULL);

  rb_free(rb);
  return 0;
}

```

--------------------------------

### Update MSYS2 Package Database

Source: https://mu.krj.st/notes/jack_win.html

Refresh the package database for MSYS2 and install any available updates using the pacman package manager. This is a prerequisite for installing other packages.

```bash
$ pacman -Syu
```

--------------------------------

### Install ALSA and PulseAudio compatibility layers

Source: https://mu.krj.st/notes/pipewire_linux.html

Installs optional PipeWire compatibility layers for ALSA and PulseAudio, ensuring seamless integration with applications using these audio systems.

```bash
$ pacman -S pipewire-alsa pipewire-pulseaudio

```

--------------------------------

### Example of MOV instruction with memory dereference

Source: https://mu.krj.st/denormal

This assembly example demonstrates the `mov` instruction, contrasting it with `lea` by showing how it dereferences a memory address to load a value into a register.

```assembly
mov rax, [1234]  ; rax = *1234
```

--------------------------------

### Example of LEA instruction for immediate value

Source: https://mu.krj.st/denormal

This assembly example shows the `lea` instruction being used to load an immediate (constant) value into a register, highlighting its basic functionality.

```assembly
lea rax, [1234]  ; rax = 1234
```

--------------------------------

### Initialize JACK Client and Register Callback

Source: https://mu.krj.st/files/sine.c

This C code snippet initializes a JACK client, sets up a shutdown callback, and registers the audio processing callback. Ensure the JACK server is running before executing.

```c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <math.h>
#include <jack/jack.h>
#define PI_F 3.14159265f

static jack_client_t *client = NULL;
static jack_port_t *port_out = NULL;
static volatile int done = 0;

static void
die(const char *msg)
{
  fprintf(stderr, "[error] %s\n", msg);
  if (client)
    jack_client_close(client);
  exit(EXIT_FAILURE);
}

static void
info(const char *msg)
{
  fprintf(stderr, "[info] %s\n", msg);
}

static void
on_shutdown(void *arg)
{
  client = NULL;
  die("jack server is down, exiting...");
}

static void
on_signal(int signum)
{
  done = 1;
}

static int
on_process(jack_nframes_t nframes, void *arg)
{
  static float phs = 0;
  jack_default_audio_sample_t *out;
  jack_nframes_t i;

  out = jack_port_get_buffer(port_out, nframes);
  for (i = 0; i < nframes; ++i) {
    out[i] = 0.1f * sinf(2*PI_F*phs);
    phs += 0.01f;
    while (phs >= 1) phs--;
  }

  return 0;
}

int
main(void)
{
  const char **ports;

  client = jack_client_open("sine", JackNoStartServer, NULL);
  if (!client)
    die("fail to open client");
  info("jack client opened");

  jack_on_shutdown(client, on_shutdown, NULL);
  info("shutdown callback registered");

  if (jack_set_process_callback(client, on_process, NULL))
    die("fail to set up process callback");
  info("process callback registered");

  port_out = jack_port_register(client, "out", JACK_DEFAULT_AUDIO_TYPE,
                                JackPortIsOutput, 0);
  if (!port_out)
    die("fail to register audio output port");
  info("output port registered");

  if (jack_activate(client))
    die("fail to activate client");
  info("jack client activated");

  ports = jack_get_ports(client, NULL, NULL,
                         JackPortIsInput|JackPortIsPhysical);
  if (ports) {
    int i;
    for (i = 0; ports[i]; ++i)
      jack_connect(client, jack_port_name(port_out), ports[i]);
    jack_free(ports);
  }

  signal(SIGINT, on_signal);
  signal(SIGTERM, on_signal);
#ifndef _WIN32
  signal(SIGQUIT, on_signal);
  signal(SIGHUP, on_signal);
#endif

  info("done! press ctrl-c to exit");

  while (!done)
    sleep(1);

  jack_deactivate(client);
  jack_client_close(client);
  return 0;
}

```

--------------------------------

### Launch QJackCtl

Source: https://mu.krj.st/notes/jack_freebsd.html

Launches the QJackCtl graphical interface for managing the JACK server.

```bash
$ qjackctl

```

--------------------------------

### Initialize JACK and Register Audio Ports

Source: https://mu.krj.st/ext

Initializes the JACK client, sets the process callback, and registers audio input/output ports based on the LADSPA descriptor. Memory is allocated for port pointers.

```c
static jack_client_t *client;
static size_t nports_in, nports_out;
static jack_port_t **ports_in, **ports_out;
static jack_nframes_t sr;

static void
jack_init(const char *name)
{
  size_t i;
  size_t n_in = 0, n_out = 0;
  const LADSPA_PortDescriptor *ports =
      descriptor->PortDescriptors;

  client = jack_client_open(name, JackNoStartServer, NULL);

  jack_set_process_callback(client, on_process, NULL);
  sr = jack_get_sample_rate(client);

  /* 1. count # input/output audio ports */
  for (i = 0; i < descriptor->PortCount; ++i) {
    if (!LADSPA_IS_PORT_AUDIO(ports[i]))
      continue;

    if (LADSPA_IS_PORT_INPUT(ports[i]))
      nports_in++;
    else if (LADSPA_IS_PORT_OUTPUT(ports[i]))
      nports_out++;
  }

  if (nports_in == 0 && nports_out == 0)
    die("no input or output audio ports");

  /* 2. allocate memory to store port pointers */
  if (nports_in > 0) {
    ports_in = calloc(nports_in, sizeof(jack_port_t *));
    if (!ports_in)
      die("fail to allocate input ports");
  }

  if (nports_out > 0) {
    ports_out = calloc(nports_out, sizeof(jack_port_t *));
    if (!ports_out)
      die("fail to allocate output ports");
  }

  /* 3. register ports to JACK */
  for (i = 0; i < descriptor->PortCount; ++i) {
    if (!LADSPA_IS_PORT_AUDIO(ports[i]))
      continue;

    if (LADSPA_IS_PORT_INPUT(ports[i]))
      ports_in[n_in++] = jack_port_register(
          client, descriptor->PortNames[i],
          JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
    else if (LADSPA_IS_PORT_OUTPUT(ports[i]))
      ports_out[n_out++] = jack_port_register(
          client, descriptor->PortNames[i],
          JACK_DEFAULT_AUDIO_TYPE, JackPortIsOutput, 0);
  }
}

static void
jack_finish(void)
{
  jack_deactivate(client);
  jack_client_close(client);
  free(ports_in);
  free(ports_out);
}
```

--------------------------------

### Open qpwgraph for audio graph visualization

Source: https://mu.krj.st/notes/pipewire_linux.html

Launches the qpwgraph application, which provides a graphical view of the PipeWire audio graph, allowing users to see and manage connections between applications.

```bash
$ qpwgraph

```

--------------------------------

### Observe HTTP GET Request for Specific Path

Source: https://mu.krj.st/mix

This HTTP GET request is sent when requesting a specific path, such as 'localhost/test'. Note the difference in the first line compared to a root directory request.

```http
GET /test HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Upgrade-Insecure-Requests: 1


```

--------------------------------

### Control Rate Numerical Example

Source: https://mu.krj.st/ctrl

This snippet provides a numerical example of control rate calculation, using a sampling rate of 48,000 and a block size of 512, resulting in a control rate of 93.75 Hz.

```plaintext
48000/512

```

--------------------------------

### Listing generated WAV files

Source: https://mu.krj.st/wave

Verify the creation of the output.wav file by listing all .wav files in the current directory. This command confirms that the program successfully generated the audio file.

```bash
$ ls *.wav

```

--------------------------------

### Initialize and Manage SDL for Framebuffer Rendering

Source: https://mu.krj.st/spectrm

Initializes SDL, creates a window and renderer, and sets up a texture for streaming pixel data. Handles SDL cleanup.

```c
static int width, height;
static SDL_Window *win;
static SDL_Renderer *renderer;
static SDL_Texture *texture;

void gui_init(void)
{
  SDL_Init(SDL_INIT_VIDEO);

  SDL_CreateWindowAndRenderer(width, height,
      SDL_WINDOW_ALLOW_HIGHDPI,
      &win, &renderer);
  texture = SDL_CreateTexture(renderer, 
      SDL_PIXELFORMAT_BGRA32,
      SDL_TEXTUREACCESS_STREAMING,
      width, height);
}

void gui_finish(void)
{
  SDL_DestroyTexture(texture);
  SDL_DestroyRenderer(renderer);
  SDL_DestroyWindow(win);
  SDL_Quit();
}
```

--------------------------------

### Send OSC Volume Command

Source: https://mu.krj.st/mix

Example command to send an OSC message to set the volume to -6dB.

```bash
$ oscsend localhost 10000 /vol f -6
```

--------------------------------

### Run the host program with a dynamic library

Source: https://mu.krj.st/ext

Execute the compiled host program, passing the path to a dynamic library as a command-line argument. The host will load the library and call its `answer` function.

```bash
$ ./host ./lib1.so
```

```bash
$ ./host ./lib2.so
```

--------------------------------

### GUI Frame and Label Drawing Example

Source: https://mu.krj.st/spectrm

Demonstrates the use of primitive drawing functions (fb_line, fb_rstr, fb_str, fb_cstr) to construct the static parts of a GUI, including an outer frame and various labels with different alignments.

```c
/* axis */
fb_line(fb, padx-1, pady,
            padx+width, pady);
fb_line(fb, padx-1, pady+height,
            padx+width, pady+height);
fb_line(fb, padx-1, pady,
            padx-1, pady+height);
fb_line(fb, padx+width, pady,
            padx+width, pady+height);

/* labels */
fb_rstr(fb, padx-4, pady, "0");
fb_rstr(fb, padx-4, pady+height-7, "1");

fb_str(fb, padx-1, pady-12, "20Hz");
/* nyq_str generated dynamically */
fb_rstr(fb, padx+width, pady-12, nyq_str);

fb_cstr(fb, padx+width/2, pady/2-4, "freq");
fb_cstr(fb, padx/2, pady+height/2-4, "mag");
```

--------------------------------

### Populating WAV Header

Source: https://mu.krj.st/wave

Prepare and populate the WAV header structure with calculated values for RIFF, FMT, and DATA chunks. This involves using `memcpy` for string identifiers and arithmetic for size and format fields.

```c
#include <string.h>
#include <stdio.h>

struct wav_hdr hdr = {0};
FILE *fp = fopen("output.wav", "wb");

/* RIFF header */
memcpy(&hdr.riff.id, "RIFF", 4);
hdr.riff.size = 36 + NSAMPLES*sizeof(sample_t);
memcpy(&hdr.riff.type, "WAVE", 4);

/* FMT chunk */
memcpy(&hdr.fmt.id, "fmt ", 4);
hdr.fmt.size = 16;
hdr.fmt.fmt_tag = 1;  /* linear PCM */
hdr.fmt.channels = NCHANNELS;
hdr.fmt.samples_per_sec = SR;
hdr.fmt.bytes_per_sec = NCHANNELS*SR*sizeof(sample_t);
hdr.fmt.block_align = NCHANNELS*sizeof(sample_t);
hdr.fmt.bits_per_sample = 8*sizeof(sample_t);

/* DATA header */
memcpy(&hdr.data.id, "data", 4);
hdr.data.size = NSAMPLES*sizeof(sample_t);

fwrite(&hdr, sizeof(struct wav_hdr), 1, fp);

```

--------------------------------

### x86 Assembly Store Instructions

Source: https://mu.krj.st/ctrl

Example of two store instructions in x86 assembly. On x86, these are not reordered at runtime.

```assembly
; a = eax
mov DWORD PTR [rip+0x2eee],eax
; b = 0
mov DWORD PTR [rip+0x2ee0],0x0

```

--------------------------------

### Initialize Wavetable (C)

Source: https://mu.krj.st/assignments/osc_s.html

Initializes a 1D wavetable with sine wave samples. This is a foundational step for wavetable synthesis.

```c
#define N 512
static sample_t tbl[N];

static void
tbl_init(void)
{
  /* divide [0,1) into N evenly spaced samples */
  float step = 1.f / N;

  for (size_t i = 0; i < N; ++i)
    tbl[i] = sinf(2*PI_F * i*step);
}

```

--------------------------------

### Get Number of Joystick Axes

Source: https://mu.krj.st/osc_i/joystick-api.txt

Uses the JSIOCGAXES IOCTL to retrieve the number of axes supported by the joystick device.

```c
char number_of_axes;
ioctl (fd, JSIOCGAXES, &number_of_axes);
```

--------------------------------

### 1D Wavetable Interpolation Example

Source: https://mu.krj.st/assignments/osc_s.html

Illustrates the linear interpolation used in a 1D wavetable, serving as a basis for understanding 2D interpolation.

```c
v0 = tbl[i];
v1 = tbl[(i+1) % N];

out = (1-fr)*v0 + fr*v1;
```

--------------------------------

### Dynamic Linking Function Substitutions

Source: https://mu.krj.st/ext

Illustrates the necessary substitutions for dynamic linking functions between POSIX systems (like macOS) and Windows.

```c
dlopen  → LoadLibrary/LoadLibraryEx
dlsym   → GetProcAddress           
dlclose → FreeLibrary              

```

--------------------------------

### Joystick Initialization and Event Reading

Source: https://mu.krj.st/osc_i/joystick-api.txt

Demonstrates how to open a joystick device and read event data. It includes the structure of a joystick event and how to interpret its components.

```APIDOC
## Initialization and Event Reading

### Description
This section covers the basic steps to initialize a joystick device and read event data from it. It includes code examples for opening the device and the structure of the `js_event`.

### Method
System Calls (open, read)

### Endpoint
`/dev/input/jsX` (where X is the joystick number)

### Parameters
#### Path Parameters
- **jsX** (string) - Required - The specific joystick device file.

#### Query Parameters
None

#### Request Body
None

### Request Example
```c
#include <fcntl.h>
#include <unistd.h>
#include <linux/joystick.h>

int fd = open("/dev/input/js0", O_RDONLY);
struct js_event e;
read(fd, &e, sizeof(e));
```

### Response
#### Success Response (200)
- **js_event** (struct) - Contains event details.
  - **time** (unsigned int) - Event timestamp in milliseconds.
  - **value** (signed short) - Event value (axis position or button state).
  - **type** (unsigned char) - Event type (button, axis, init).
  - **number** (unsigned char) - Axis or button number.

#### Response Example
```c
struct js_event {
    __u32 time;
    __s16 value;
    __u8 type;
    __u8 number;
};
```

### Error Handling
- `open()` can fail if the device does not exist or permissions are denied.
- `read()` can block if the device is opened in blocking mode and no events are available.
```

--------------------------------

### Get JACK Buffer Size

Source: https://mu.krj.st/notes/jack_macos.html

Retrieves the current buffer size of the JACK server. This command requires the JACK server to be running.

```bash
$ jack_bufsize

```

--------------------------------

### 64-bit Global Variable Declaration

Source: https://mu.krj.st/ctrl

Declares a 64-bit unsigned integer variable 'p'. This variable is used in a multithreaded example to demonstrate torn reads.

```c
uint64_t p;

```

--------------------------------

### Link the host program with the dynamic linking library

Source: https://mu.krj.st/ext

When compiling the host program, link it with `libdl` using the `-ldl` flag to enable dynamic loading functionalities.

```bash
$ gcc -o host host.c -ldl
```

--------------------------------

### Example: Disabling Denormals for Performance (32-bit x86)

Source: https://mu.krj.st/denormal

Demonstrates using the denormal handling library to disable denormals before a computation loop on a 32-bit x86 system, then restoring the original state. This can significantly improve performance.

```c
// disabled_32.c: denormal disabled (32-bit)
#include <stdio.h>
#include <float.h>
#include "denormal.h"

#define N 100000000

int main(void)
{
  size_t i;
  float mem = 2*FLT_MIN;
  fpcr_t fpcr;

  fpcr = denormal_disable();

  for (i = 0; i < N; ++i)
    mem = 0.999f * mem;

  printf("%g\n", mem);

  denormal_restore(fpcr);
  return 0;
}

```

--------------------------------

### Compile Sine Oscillator Program

Source: https://mu.krj.st/osc_i

This command compiles the `sine_simple.c` program, linking against the JACK and math libraries. Ensure you have the JACK development libraries installed.

```bash
$ cc sine_simple.c -o sine -ljack -lm
```

--------------------------------

### Main Thread DFT Input Preparation

Source: https://mu.krj.st/spectrm

This function runs in the main thread to prepare input for the DFT. It reads samples from the ring buffer, ensuring enough data is available, and then executes the DFT plan. Requires linking with -lfftw3f.

```c
#define N 512
#define FFT_SIZE (N*sizeof(sample_t))
static sample_t *fft_in;
// note that we are using the float variant of fftw
// it needs to be linked with -lfftw3f
static fftwf_complex *fft_out;
static fftwf_plan fft_plan;

static int
render(void)
{
  size_t avail;

  // read data from audio thread
  avail = rb_read_space(rb);
  if (avail < FFT_SIZE)
    return 0;
  rb_read_advance(rb, avail - FFT_SIZE);

  if (!rb_read(rb, fft_in, FFT_SIZE))
    return 0;

  // execute fft
  fftwf_execute(fft_plan);

  // ...
}

```

--------------------------------

### Initialize Wavetable with Sine Values (Method 1)

Source: https://mu.krj.st/osc_ii

Initializes a static wavetable array by dividing the range [0,1) into N evenly spaced samples and calculating the sine for each. Ensure PI_F is defined.

```c
#define N 512
static sample_t tbl[N];

static void
tbl_init(void)
{
  /* divide [0,1) into N evenly spaced samples */
  float step = 1.f / N;

  for (size_t i = 0; i < N; ++i)
    tbl[i] = sinf(2*PI_F * i*step);
}


```

--------------------------------

### Compile sine.c with JACK flags

Source: https://mu.krj.st/notes/jack_linux.html

Compiles the sine.c program using gcc, linking against JACK libraries. Ensure pkg-config is available and JACK is installed.

```bash
$ gcc sine.c $(pkg-config --cflags --libs jack) -lm

```

--------------------------------

### C Static Variable Example

Source: https://mu.krj.st/osc_i

Demonstrates the behavior of static variables in C. A static variable is initialized only once and retains its value across function calls.

```c
#include <stdio.h>

void func(void)
{
  static int x = 0;
  // `x` is initialized only once across three
  // calls of `func` and the variable will get
  // incremented three times after these calls.
  // The final value of `x` will be 3.
  x++;
  printf("%d\n", x);
}

int main(void)
{
  func();  // prints 1
  func();  // prints 2
  func();  // prints 3
  return 0;
}

```
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