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Stream Looper

Marc Joliet marcec@gmx.de

Introduction

Stream Looper is a simple looping program. It continuously records an audio stream into a buffer and loops an arbitrary contiguous region within it. Stream Looper is written in FAUST.

I wrote this purely for fun and to try out the FAUST DSP language. I do not claim any originality here. In fact, Kluppe implements the functionality of Stream Looper (in addition to loads of other features) in a nice graphical way. However, I did not want to develop a complex application in the first place; I just wanted to try writing a simple stream looper in FAUST.

Originally, I had imagined it to be a sample based looper. I formulated the gist of it as follows:

Here's an idea: a simple sampler that has an adjustable auto-repeat and that syncs to a master beat, so you can control breakbeats with a knob. It should be able to load multiple samples and have one JACK output per sample.

Of course, by now I don't know what I meant by "auto-repeat". However, I suppose I was writing about what is referred to as "Period" below. Anyhow, as implemented it is obviously not a sampler. It is probably best to instead compile Stream Looper into an LV2 plug-in and load it into one of the many pre-existing samplers/sequencers.

Compilation

You can either use the provided SCons based build system, whose invocation in this case is simply

scons

The SCons build system will automatically pass appropriate options to the FAUST compiler, such as -vec to produce auto-vectorisable code. The default FAUST architecture is jack-qt, see the output of scons --help for more information.

This relies on an externally available FAUST SCons tool that I found here.

Of course, you can always just use any of the myriad of faust2* scripts that are distributed with FAUST. This requires more knowledge of the FAUST options, though (see faust --help).

Usage

As mentioned above, Stream Looper works by recording an input signal into an internal buffer and looping within that buffer. Playback never stops.

UI-independent Controls

FAUST can generate various types of programs, and they will share the same controls, be it as command-line options, Pd messages, or graphical sliders. The following description holds for all of them.

You can control two things: the way the loop is played, and the way it is recorded. Specifically, you control the region within the buffer in which the read and write pointers loop. In both cases, there there are two sliders to control this behaviour, put into the groups "Recording" and "Playback":

  • "Period" sets the duration of the loop, and
  • "Start" defines the loop's starting point within the buffer.

Moving the "Playback/Start" slider around can produce an effect not unlike vinyl scratching, with the difference that the buffer is constantly being played back. The "Recording/Period" slider can be used to increase the rate at which the playback loop changes. The "Recording/Start" is a bit pointless, but can produce glitch effects. Usually you won't want to change it, but you can if you want to.

Furthermore, there are three check boxes:

  • "Bypass" bypasses the internal buffer and plays the input signal directly
  • "Pause Recording", well, pauses recording so that you can play around with a static buffer ("Playback/Start" makes the most sense here).
  • "Limit to Rec Period" limits the playback pointer period to the write pointer period. This is so you can decrease the write pointer period and not have old material in the buffer start to play.

OSC controls

Stream Looper can be controlled via OSC thanks to FAUST's built-in support. You can find the available addresses, their current values and their value range by sending a get message to the wildcard address /stream_looper/*, which yields:

/stream_looper//Playback/Period 32768 1 32768
/stream_looper//Playback/Start 1 1 32768
/stream_looper//Recording/Period 32768 1 32768
/stream_looper//Recording/Start 1 1 32768
/stream_looper/Bypass 0 0 1
/stream_looper/Limit_to_Rec_Period 1 0 1
/stream_looper/Pause_Recording 0 0 1

NOTE for those who know FAUST: the double slashes in the first four addresses arise from the use of an unnamed hgroup().

MIDI controls

In addition to the controls available via OSC, all of the parameters can be controlled via MIDI CC messages, at least for the FAUST architectures that make use of the UI element meta-data. In FAUST version 0.9.58, these are, as far as I can tell: dssi, lv2, lv2synth, ms-jack-gtk and vsti-mono.

The CC# to UI control mapping is:

  • 0 maps to "Playback Period"
  • 1 maps to "Playback Start"
  • 2 maps to "Recording Period"
  • 3 maps to "Recording Start"
  • 4 maps to "Pause"
  • 5 maps to "Bypass"
  • 6 maps to "Limit to Rec Period"

Logitech RumblePad ™ 2 Pure Data UI

For my own use I wrote a Pd UI through which you can control Stream Looper with a RumblePad 2 controller. It has two variants:

  1. One that uses Stream Looper as a Pd external, called rumblepad_ui.pd. In this case, you must compile Stream Looper with faust2puredata or scons FAUST_ARCHITECTURE=puredata ... first before you can use it. Technically you could also use faust2pd, if I understand it correctly, as the Pd object name stays the same, but it is superfluous for the purposes of this UI.
  2. One called rumblepad_osc_ui.pd that communicates with Stream Looper via OSC, e.g., when compiled as a stand-alone JACK application.

The controller mappings are set up as follows:

  • The left joystick controls "Period" for the playback (vertical axis) and recording group (horizontal axis).
  • The right joystick controls "Start" for the playback (vertical axis) and recording group (horizontal axis).
  • Button 1 switches "Pause Recording" on when held down.
  • Button 2 toggles "Bypass" every time it is pressed.
  • Button 3 toggles "Pause Recording" every time it is pressed.
  • Button 4 toggles "Limit to Rec Period" every time it is pressed.
  • Button 9 toggles whether the vertical axis of the right joystick is ignored.
  • Button 10 toggles whether the horizontal axis of the right joystick is ignored.

"Pause Recording" and "Limit to Rec Period" are off by default, while "Bypass" is on by default so that moving the joystick doesn't constantly change the playback. Also, since its effects are usually unwanted, the right joystick is ignored by default.

TODO

I still want the following features:

  • Sync to beat, in which case the "Period" slider will function in terms of bars or similar unit. Ideally, "Pause Recording" will wait until the bar is finished before pausing.
  • Perhaps add a slider to control the amount of smoothing on the "Start" slider.
  • Add LV2 support to the build system. Until then, use the faust2lv2 script that comes with FAUST.
  • Fix the artifacts that arise when changing the write period. Possible solutions (disregarding implementation):
    • set both the read and write period to maximum as long as the slider is being held by the mouse
    • only update the write period once the pointer is at zero again
    • ...
    • Actually, I'm not sure anymore whether this is really a problem.