dmckminard/porc

Python Open Room Correction (PORC)

Python Open Room Correction (PORC)

PORC now includes mixed-phase compensation (see below)!

DSP Loudspeaker-Room correction filter wizard; transfer function modeling and equalization by fixed-pole parallel filters. Algorithm ported to Python by Mason A. Green, based on the work of Dr. Balazs Bank: http://home.mit.bme.hu/~bank/parfilt/

More details about Dr. Bank's parallel filter can be found in the papers:

Balazs Bank, "Perceptually Motivated Audio Equalization Using Fixed-Pole Parallel
Second-Order Filters," IEEE Signal Processing Letters, 2008.

http://www.acoustics.hut.fi/go/spl08-parfilt

Balazs Bank, "Direct Design of Parallel Second-order Filters for
Instrument Body Modeling," International Computer Music Conference,
Copenhagen, Denmark, Aug. 2007.

http://www.acoustics.hut.fi/go/icmc07-parfilt

Mixed-Phase Compensation references:

Alberto Carini, et al, "Mixed Time-Frequency approach for Multipoint
Room Response Equalization," AES 45th International Conference, 2012

Defrance & Polak, "Measuring the mixing time in auditoria," Acoustics
Paris 2008

Required Python dependencies:

1) Python 2.7
2) Scientific Python: SciPy, Numpy, & Matplotlib

The easiest install method on Windows is simply to install the continuum.io Anaconda package.

Measurement

One needs to measure the log-frequency impulse response of your speakers with a calibrated Electret Measurement Microphone, e.g. Dayton Audio EMM-6. Software such as Room EQ Wizard (REQ), Holm Impulse, or Arta may be used for this purpose: http://www.hometheatershack.com/roomeq/

Usage

porc.py [-h] [--mixed] [-t FILE] [-n NTAPS] [-o OPFORMAT] input_file output_file

python porc.py -t tact30f.txt -n 6144 -o bin l48.wav leq48.bin

Use the -h flag for help!

PORC has been tested successfully on both Linux and Windows 7 with Python 2.7. Linux depenency install is fairly straightforward. Windows install packages are available for all dependencies.

Target Response

The default target curve for PORC is flat. Included in the data directory are a number of target curves. Experiment to suit your listening preferences. Use the [-t] flag to load a target file.

One may also target a flat curve, and then use separate parametric equalization for bass boosting and other pschoaccoustic preferences.

For further reference, the B&K House Curve is a good place to start. Read "Relevant loudspeaker tests in studios in Hi-Fi dealers' demo rooms in the home etc.," Figure 5: http://www.bksv.com/doc/17-197.pdf

Mixed-Phase Compensation

To use mixed-phase compensation, one needs to specify the [--mixed] flag. One also needs to modify the Room Impulse Response (RIR) to remove leading silence (zeros) before the main impulse. You can easily do this with Audacity or REQ.

Example:

python porc.py --mixed -t tact30f.txt -n 6144 -o bin l48.wav leq48.wav

Have some patience with this method. The convolution takes a few CPU cycles.

PC Convolution

Suggestions:

Windows (foobar2000 convolver) Linux (jconvolver w/ jcgui & Jack)

You may need to merge left and right channels into a single stereo .wav

sox -M le148.wav req48.wav equalizer.wav

OpenDRC Convolution

Use -o bin flag to set binary 32bit IEEE floating point mono file format output for OpenDRC.

TODO

Implement algo to automatically remove leading silence (zeros) from RIR.
Add a GUI Frontend (pretty interactive graphs, drawing target curve, etc...)
Update this page with better documentation!

Contact

Complaints, suggestions, bugfixes: mason dot green at gmail