Mighty Looper

Mighty Looper project is an attempt to build an open source, portable, low-cost, 2-channel, multi-track audio looping machine that allows to operate within 2 individual loop phrases (verse/chorus). It is implemented in Pure Data extended by C libraries, runs on Raspberry Pi and is controlled by Arduino based controls and Android app as graphical interface. The looper is supposed to be used in a single person performance with multiple instruments.

The project is currently still under development.

What it does (will do)

Here are main features and functionalities of the looper:

• 2 separate phrases (verse/chorus) possible to switch between while each of them:
  • consists of 8 tracks in 2 channels (4 tracks per channel)
  • is possible to individually reset and start over
• 2 separate channels each possible to:
  • adjust volume
  • mute/unmute
  • switch bypass ON/OFF
• 4 separate tracks per channel each capable of
  • recording with infinite overdubs
  • UNDO/REDO function
  • switching looping ON/OFF
  • muting/unmuting
  • resetting
  • adjusting volume

How it works (will work)

The looper is designed to make recording and playback of loops comfortable and easy in terms of loop length accuracy. For achieving this the following concepts are implemented:

• built-in click - Tempo (for both phrases) and time signatures (for each phrase separately) are set before the looper is initialized (before the first track is recorded).
• scheduled actions - Most of recording and playback related actions are aligned with the click. Instead of action taking effect immediately after user triggers it via footswitch it is scheduled (flagged) to the next specified event in the click flow (usually the beginning of new loop cycle). This eliminates the need for precise footswitch presses while ensures loops to be perfectly aligned with the click. The following are actions with corresponding triggering click events:
  • start recording of the first track - the beginning of bar (according to time signature) after 2 full bars have passed (not counting the bar in which the footswitch was pressed)
  • stop recording of the first track - the first beat of the click after the footswitch was pressed (this means that loop lenght is not strictly defined by time signature, user can make also loops which end with incomplete bars)
  • start recording of other tracks - the beginning of loop's new cycle
  • stop recording of other tracks - recording is automatically stopped at the end of current loop's cycle (unless uses stops it manually - this action is not aligned with the click)
  • switch ON/OFF looping of track - the beginning of loop's new cycle
  • UNDO/REDO of last track's layer - the beginning of loop's new cycle

NOTE: The looper may be extended by free-length recording mode without using click in the future to make its use more general.

How it's (will be) controlled

Arduino controls

There are 4 footswitch boxes (2 for each channel - 1 for recording, 1 for playback) each with 4 switches (1 for each track of corresponding channel).

• recording switches have following press types mapped to actions:
  • single press - flags/unflags recording of corresponding track if it is not being currently recorded, otherwise stops recording
  • double press - TBD
  • long press - flags recording to both phrases simultaneously of corresponding track if it is not being currently recorded, otherwise cancels recording
• playback switches have following press types mapped to actions:
  • single press - flags switching looping ON/OFF of corresponding track
  • double press - mutes/unmutes corresponding track
  • long press - UNDO/REDO last recorded layer of corresponding track

There is 1 footswitch box with 3 switches:

• 1 for each channel with following press types mapped to actions:

  • single press - flags/unflags switching looping ON/OFF of corresponding channel
  • double press - mutes/unmutes corresponding channel
  • long press - TBD

• 1 for switching between phases by single pressing

• 8-digit 7-segment display shows progress of each track loop

Android app

Role of graphical user interface is played by Android app that can:

• set tempo and time signatures for click
• switch click ON and OFF
• adjust volumes for master out, phones out, tracks, channels and click
• mute/unmute tracks, channels, master, etc
• switch ON and OFF bypassing of each channel to output
• perform all the controlling actions that can be done by Arduino controls as well
• reset Looper
• turn looper OFF
• display loop progress for each track
• TBD

How it's (will be) put together

The looper logic is implemented in Pure Data patch running on Raspberry Pi 3 while it is being controlled by the sketch running on Adruino with footswitches connected and by Android app providing all needed options for setting looper as well as controlling it. RPi and Arduino talk to each other via serial port. Android app and RPi talk to each other over bluetooth.

As an audio interface a sound card compatible with RPi which has stereo input and stereo output is required. Here are some working and not working sound cards listed. I've tried several of those little cheap USB sound cards with rather bad results. Behringer UFO202 worked quite well with low latency but so far I had the best results with Audio Injector that appears to work glitch-free with the latency as low as 5ms.

Credits

In the initial stage of this project I drew a lot of inspiration from GuitarExtended blog which provides very comprehensive guide on how to make guitar effects in Pure Data running on Raspberry Pi. Very well done! Thanks!