Digital IR measurements from Matlab

Use Jack to measure impulse responses from digital system directly from Matlab.

Installation

1. Download & install Jack: http://jackaudio.org
2. Put the provided function in a path where Matlab can find them

Setup

1. Set up jackConfig (See digiIR.m for full example)
2. Run startJack(configJack)
3. Connect your application / system to Jack
4. Run setupJack(configJack)

Usage

If the setup is complete, you may probe your system by simply running

[ y, t ] = recordImpulse( 1, recorder, jackConfig);

jackConfig

jackConfig is a struct that contains all necessary configuration variables:

jackConfig.jackpath = '/path/to/jack/'; % Default: /usr/local/bin/
jackConfig.App = 'APP'; % Default: Live
jackConfig.fs = 8000 - 192000; % Default: 44100
jackConfig.nBits = 4 - 32; % Default: 16
jackConfig.nChannels = 1 - 128; % Default: 2
jackConfig.framesize = 16 - 1024; % Default: 256
jackConfig.verbose = true/false; % Default: true
jackConfig.IDi = int; % Only after setupJack()
jackConfig.IDo = int; % Only after setupJack()

Probably stick to defaults for now.

Plotting

Several functions for convenient plotting are provided:

• plotIR( y, t ) plots the IR y in the time domain.
• plotSpectrogram( y, window, overlap, n, fs ) plots a spectrogram (frequency spectrum over time). The colormap is matplotlib's new default viridis.
• plotFFT( y, fs ) plots the overall frequency spectrum.

They employ getSpectrogram( y, window, overlap, n, fs ) and easyFFT( y, fs ) respectively.

OSX only (for now)

Only tested on Mac OSX 10.10.5 with Jack 1.9.10 and Ableton Live. For non-OSX, maybe try adjusting the -d coreaudio backend driver in the startJack.m function.

Christoph Hohnerlein

mail@chrisclock.com, chohner@ccrma.stanford.edu

Nov 12, 2015