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Faust Integration with the SHARC Audio Module

Overview

Faust (Functional Audio Stream) is an open-source, functional programming language, specifically designed for real-time audio signal processing and synthesis. Faust generates C++, as well as other target languages, for signal processing applications.

The Faust library provides a rich set of audio DSP objects that can be used in creating DSP algorithms. Using Faust, it is possible to quickly create large algorithms that take advantage of the computing power available on the SHARC Audio Module platform.

Not only can Faust generate efficient inner loops in C++, it also:

Can generate test GUIs for prototyping algorithms
Can generate easy-to-read hierarchical block diagrams directly from the Faust source, which graphically illustrate signal flow and processing.
Provide a runtime system that supports MIDI for both voice allocation and parameter control.

Useful Faust References

This document will not go into detail about the Faust language. There are a number of good references and tutorials for Faust. Here are some useful references for learning more about Faust.

The Faust Compiler

The new Faust Online Editor can be used to edit, compile, and run Faust code from any modern Web Browser with WebAssembly support. All prototyping is done in a web browser and the browser can export C++ code targeted for the SHARC Audio Module platform.

Recommended Browsers

Chrome (Recommended)
Firefox (Note: MIDI is not currently supported)

faust2sam

Faust programs may be targeted for many different platforms via what is known as “an architecture”. Internally the script faust2sam calls the Faust compiler using an architecture that is specific to the SHARC Audio Module platform. When an algorithm is compiled using faust2sam, three C++ source code files are generated for the SHARC Audio Module platform. These files may then be inserted into the baremetal framework Cross Core Embedded Studio (CCES) workspace to be compiled into an algorithm that runs on the SHARC Audio Module platform.

Note: While it's possible to install and run faust2sam locally on your Linux or macOS machine we generally recommend the use of the Faust Online Editor since it runs in your web browser and is available on all platforms including Microsoft Windows.

Hardware Setup for Faust

In order to have a successful experience using Faust, certain hardware will be needed.

Hardware Needed

ICE-1000 or ICE-2000
SHARC Audio Module Platform and accompanying power supply
Audio Project Fin
3.5mm stereo cable or equivalent
Powered speakers
Device capable of sending MIDI signals such as a MIDI keyboard controller
MIDI cable

Hardware Connections

Attach the Audio Project Fin to the expansion interface of the SHARC Audio Module Platform (P4/P5)
Connect the 3.5mm jack from the powered speakers to LINE OUT of the SHARC Audio Module
Connect the 3.5mm jack coming from the audio source to LINE IN of the SHARC Audio Module
Connect the end of the MIDI cable to MIDI IN of the Audio Project Fin
Connect the cable of the ICE-1000 or ICE-2000 to the DEBUG header on the SHARC Audio Module
Connect the end of the power supply to P3 of the SHARC Audio Module

Faust with the CCES Bare Metal Framework

The SHARC Audio Module Bare Metal framework is a light-weight C / C++ framework designed for efficient audio signal processing using the ADSP-SC589 processor on the SHARC Audio Module main board. Users can easily run their Faust algorithms using the bare metal framework.

Adding Faust files to the Baremetal Framework

Faust algorithms can be added to this framework in the faust directory.

The CCES Baremetal Framework has a subproject directory for each processor core:

<PROJECT_NAME>_Core1
<PROJECT_NAME>_Core2

For each project directory there is a directory where the three source files created from the Faust online editor should be placed.

<PROJECT_NAME>_Core1/src/faust
<PROJECT_NAME>_Core2/src/faust

Each core can be running a different Faust algorithm.

Typical Faust Bare Metal Configuration Settings

Bare Metal Project Wizard Setup

It is easy to get up and running with a new project in CrossCore Embedded Studio using the bare metal project wizard.

The following options should be selected when using the wizard:

Give the project a meaningful name, click Next.
Choose the Audio Project Fin on the Expansion Fin Selection page because it is used in all tutorials, click Next.
Click Next on the A2B Module Selection page without making any changes.
On the Faust Support page choose which cores will be running Faust, click Finish.

No other options need to be changed.

Configuration File Setup

This section is only needed if the bare metal project wizard is not used or to update the configuration file if there was a mistake when using the wizard.

In addition there is a header file that is common across all cores called audio_system_config.h. In this file the following pre-processor macros should be set. The example below indicates that a Faust algorithm will only be running on Core1 and that Core2 will be simply passing audio to the codec.

#define SAM_AUDIOPROJ_FIN_BOARD_PRESENT TRUE
 
#define FAUST_INSTALLED TRUE
 
#define USE_FAUST_ALGORITHM_CORE1 TRUE
 
#define USE_FAUST_ALGORITHM_CORE2 FALSE

Compiling and Running the Algorithm in CCES

This document will not go into extensive detail on how to use CCES. Please go through the CCES Getting Started Guide if looking for more detailed information on using CCES. However here are some brief notes on how to work with this algorithm.

Copy the Faust C++ source files to the faust directory for the core that the algorithm will run on.
Set the audio_system_config.h preprocessor macros as described.
Open the workspace with CCES.
Use File> Import> General> Existing Projects into Workspace to import the projects for each core into the workspace.
Compile with Project> Build Project (This may take a few minutes)
Connect the host computer to the SHARC Audio Module with an ICE-1000 or ICE-2000 emulator.
Make hardware connections as described in Hardware Connections
Create a Debug Configuration per the CCES instructions.
Run the compiled algorithm on the SHARC Audio Module with Run> Debug
Send MIDI signals depending on the algorithm created

MIDI in Faust

Mapping MIDI messages to Faust Control

Faust has a number of meta data conventions for mapping MIDI messages into Faust control. Below is the simple MIDI controlled sawtooth synth, which illustrates how this control mapping is done. In the example below nentry() is a numerical entry object that can be mapped to receive specific MIDI values. A number of metadata values are reserved to have specific mapping functions.

freq – If a MIDI noteOn event is received it’s MIDI keyNumber is mapped to a frequency.
bend – if a MIDI pitchBend message is received it is mapped to a bend value.
gain – if a MIDI noteOn message is received it’s velocity value is mapped to a gain value which ranges from [0 .. 1.0]
gate – if MIDI noteOn/noteOff messages are received they are mapped to a gate value (0/1)
[midi:ctrl 1] – A Faust control (slider, etc.) can be mapped to listen to a MIDI continuous controller.

MIDI Conventions for Audio Project Fin

The pots and push buttons on the Audio Project Fin can be used to control key algorithm parameters. The pots and push button switches are mapped to default continuous controllers.

Pot Mapping

Pot	CC
`HADC0`	`CC-2`
`HADC1`	`CC-3`
`HADC2`	`CC-4`

Push Button Switch Mapping

PB	CC
`SW1`	`CC-102`
`SW2`	`CC-103`
`SW3`	`CC-104`
`SW4`	`CC-105`

The algorithm examples that are provided use these conventions. For example, the effects algorithm is “echo : flange : chorus : reverb”. For this algorithm each of the four push buttons turns on a different effects unit. The first pot is the echo feedback, the second pot is the reverb room size and the third pot is the reverb damping.

Typical Workflow

The typical workflow using faust to design algorithms for the SHARC Audio Module is:

Open the Faust online editor.
Name the *.dsp file appropriately for the algorithm being created.
Create the algorithm in Faust. MIDI control can be attached to the algorithm in the Faust code using the MIDI metadata mechanism discussed in MIDI in Faust.
Compile and run the Faust program using the button

Compiling within CCES can take a while so it is recommended to iterate through changes using the Faust editor until comfortable with the algorithm

Once the developer is satisfied with the algorithm faust2sam (run in the background) can be used to generate a set of C++ files for the algorithm that are intended to be used with a CCES framework.
Click the Export/compile to a specific platform button
In the second dropdown box, choose sam and then Export
Click on the QR code that shows to download the files
These 3 source files can be copied to the faust directory in the CCES framework. The framework can then be compiled and downloaded to the SHARC Audio Module.

Here is a block diagram of how the code for the virtual analog synthesizer demo and the effects chain is organized.

Example Workflows

Prev.: Hardware ReferenceUp: SHARC Audio ModuleNext.: MicroPython Overview

Wiki

Analog Devices Wiki

Table of Contents

Faust Integration with the SHARC Audio Module

Overview

Useful Faust References

The Faust Compiler

faust2sam