Formula

The square wave has a faster decay towards higher partials than the sawtooth. It can be found in spectra of wind instruments.

• only odd harmonics

• constant sign

Interactive Example

Like the sawtooth, the square wave shows the occurrence of ripples at the steep edges of the waveform. The higher the number of partials, the denser the ripples. This is referred to as the Gibbs phenomenon.

Faust Code

The Faust project features a rich set of properly documented examples. Nevertheless, this class has an accompanying Git Repository for code snippets and small tutorials.

Links

There are a couple of links, which reappear as references in this lecture or can be used as additional resources.

• CCRMA website of Julius Smith

• Faust Tutorials by Romain Michon

Recommended IDEs

• Spyder

The Arduino

For all examples in this section, the Arduino UNO is used. The documentation on the official Arduino website covers all details on the connection possibilities and many examples to get started. The most important bit of information for most tutorials and basic applications is the pinout map:

Besides power and ground pins, the following connections are of interest for these examples:

• 6 analog inputs (0-5V)

• 14 digital pins (in and output mode can be set for each pin)

• 5 PWM output pins

• serial receive

• serial transmit

The Sensor

This very first step shows how to use basic sensors with the Arduino. These sensors are variable resistors, which change their conductivity based on physical quantities. Examples are temperature, distance or force. The following examples us a light dependent resistor (LDR). The brighter the light it is exposed to, the lower its resistance.

The Voltage Divider

In order to use the light dependent sensor in a measurement setup, a so called voltage divider is needed. It compares the variable resistor R1 (in this case the LDR) with a fixed resistor R2:

For a full use of the voltage range, R3 needs to be chosen properly. The voltage measured at the output depends on the reference voltage of 5V and the ratio between the two resistors:

$$ V_{out} = 5V \frac{R_2}{R_1 + R_2} $$

Some components, like potentiometers and faders, have the voltage divider integrated and thus have three pins for connection. They do not require an additional resistor.

Breadboard Wiring

The above-shown circuit can be realized using all components, a mini breadboard and three jumper cables. The documentation on the original Arduino website (Getting Started with Arduino introduces the board with all its connection capabilities in detail. For this example, we need a small breadboard, the LDR, one resistor and three jumper cables. A $100 \Omega$ resistor is chosen. For first steps, the Arduino can be powered via USB, which will also be used to read the sensor data into the Arduino serial monitor.

Arduino Code

The easiest way to program an Arduino is the dedicated Arduino IDE, which is available for all major operating systems. Install and use instructions are thoroughly documented on the official Arduino website.

The Arduino code for testing this sensor circuit is minimalistic. Like most Arduino sketches, basic setup is carried out in the setup() function on boot. In this case, the serial interface is started with a baud rate (speed in symbols per second) of 9600 bauds. Afterwards, the loop() function is carried out infinitely. It reads the given voltage at the selected pin A0 and prints it to the serial output.

Follow the instructions on the Arduino website to upload the below code to your board. In general, the serial port of the board needs to be selected in the IDE's dropdown manual, alongside the Arduino model - in this case the Arduino UNO.

void setup() {

Serial.begin(9600);
}

void loop() {

int sensorValue = analogRead(A0);

Serial.println(sensorValue);

delay(5);
}

Without any manipulation, the values from the analogRead() function range from 0 to 1024, since the Arduino analog-digital converters have 10 bit resolution:

$$ N = 2^{10} = 1024 $$

Exercise

Max Audio Effects

Dragging the default Max Audio Effect into a track gives a basic patch connecting audio inlets (plugin~) with audio outlets (plugout~). Any processing can be inserted in between.

The following example uses the degrade~ object inside a Max Audio Effect.

Max Instruments

The default Max Instrument can be dragged into a MIDI channel. It gives a patch with a midiin object to receive any incoming MIDI data and the plugout~ object to send audio into Live. Unlike the default Audio Effect, this patch is not functional.

Like the midiin object, other MIDI objects in Max can also be used inside Max For Live devices. The following mini saw example shows how to control a patch with MIDI from Live, using the notein and the ctlin objects.

Automation to Max for Live

The Inspector View

Although controlling Max for Live with MIDI is a good solution for many applications, Device Parameter Automation offers more flexibility and can also be used in audio channels. Most parameters in a Max for Live patch can be activated for automation, by editing inside the number inspector:

The following adjustments need to be made:

• Parameter Mode Enable: check

• Name (long/short): foo

• Type: match parameter

• Range: match parameter

• Modulation Mode: match parameter

• Parameter Visibility: Automated and Stored

Track Automation

After making the Max for Live parameters ready for automation, the general automation mode needs to be enabled in the Arranger view (the tiny blue button above the audio track). Afterwards, each tack shows the available automation parameters and they can be edited.

Clip Automation

The automation panel in the clip view gives access to all activated Max for Live parameters. This kind of modulation is tightly linked to the audio material, which can be both helpful and complicated.

Find more information on live parameters: https://docs.cycling74.com/max5/vignettes/core/live_parameters.html

Binaural Listening

Two-ear (binaural) listening encodes information on the direction and distance of a sound source by several cues. Figure 1 shows a listener with a sound source and its properties azimuth elevation and distance.

Interaural cues are based on the signal of both ears, more precisely their differences. They are in particular relevant for the horizontal Localization, respectively the azimuth:

• interaural time differences (medium frequencies)

• interaural level differences (high frequencies)

• interaural phase differences (low frequencies)

In addition to the interaural cues, the coloration gives information on the elevation of a sound source, as well as on opposing azimuth angles which have identical interaural cues.

Binaural Recording Technology

HRTF Generation

Individual

Generic

Binaural Room Impulse Responses

References

Ansible Without SSH Keys

apt-get install sshpass

Playbooks

Instead of logging in in every machine via SSH, we write an Ansible playbook that describes all tasks in a YAML file.

---
- name: Installing packages
  hosts: web
  become: yes
  gather_facts: no
  tasks:
    - name: Install git
      apt:
          name: git
          state: present
          update_cache: yes
    - name: Install ALSA
      apt:
          name: alsa
          state: present
          update_cache: yes
    - name: Install ALSA Dev
      apt:
          name: libasound2-dev
          state: present
          update_cache: yes
    - name: Install Jack
      apt:
          name: jackd2
          state: latest
          update_cache: yes

By default Ansible logs into every machine via SSH. hosts: web tells ansible to execute following tasks on all machines in the inventory group web. Installing packages with APT requires superuser permissions. become: yes tells Ansible to become root. The default method for this is sudo.

The biggest benefit over shell scripts is that it is possible to describe the state of a machine. In the example four packages will be installed. Only jackd2 will be updated if it is already present.

---

Inventory

For executing our new playbook Ansible needs to know what machines are in our inventory. The inventory can be written in INI or YAML syntax.

[local]
localhost

[web]
google.de
facebook.de

The default location for your inventory file is /etc/ansible/hosts.

For more information for creating your inventory see the official user guide.

---

ansible.cfg

A separate inventory file can be set for your project in an Ansible configuration file ansible.cfg:

[defaults]
inventory = hosts
ansible_ssh_user = studio
sudo_user = studio

This file sets the location of your inventory file to ./hosts. Furthermore the default SSH user as well as the sudo user gets set to studio.

---

Executing a Playbook

Executing our playbook file install_basic.yml:

ansible-playbook install_basic.yml -k -K

For this to work every machine in group web must have a user studio with the same password. The flag -k lets Ansible ask for a SSH password. -K is for the sudo password.

If there's a SSH key for user studio on all machines, no SSH password has to be typed, but the password for sudo is still necessary.