Two popular methods of room correction are Room EQ Wizard (REW) and Dirac Live™. In this application note, we will compare and contrast these two methods.
What is Room EQ Wizard?[Top]
Room EQ Wizard (http://www.roomeqwizard.com) is a freeware acoustic measurement and analysis program. It runs on Windows, Mac, and Linux computers. In addition to its comprehensive acoustic analysis capabilities, it has the ability to generate parametric equalizer filters to correct a measured acoustic response. You can either correct towards a flat response or to a specified "target". These filters can be written to a file and then loaded into the PEQ block of a compatible miniDSP plugin.
Here, for example, is a measurement of a woofer (top plot in darker blue), the auto-generated correction filter (lowest plot in green), and the corrected response (middle plot in lighter blue):
In this example, the target response is flat (from 80 Hz to 1000 Hz). For additional information on how to use the Auto EQ feature, see the app note Auto-EQ tuning with REW. (The example above is a bit atypical - we have chosen it to make it easier to see the three plots mentioned.)
What is Dirac Live?[Top]
Dirac Live™ is a room correction algorithm developed by Dirac Research AB of Sweden. It uses a very powerful algorithm to analyze a set of nine measurements taken around the listening area and to generate a correction filter. The correction is implemented using what Dirac Live call mixed-phase filters. (More on that below.)
Dirac Live Calibration Tool corrects the measured in-room amplitude response to a specified "target curve." Usually, it has a rise in the bass and a slight fall in the treble. This image shows the uncorrected response of left and right speaker in blue, and the corrected response in green (the plots are an average of nine measurements):
Dirac Live Calibration Tool also corrects the time domain response of the loudspeaker. The next diagram illustrates a "perfect" impulse response of a loudspeaker, the measured impulse response, and the impulse response after correction with Dirac Live. This impulse response correction enhances stereo imaging and realism.
The key differences[Top]
REW uses IIR filters, while Dirac Live uses mixed-phase filtering - in effect, a combination of IIR and FIR filters. FIR filters are more powerful than IIR filters, but more expensive to implement. See the app note FIR vs IIR filtering for information on the differences between these two different types of digital filter.
Dirac Live Calibration Tool uses nine different measurements around the listening area and searches for optimizations that it can perform across the whole listening area. With REW, you can take multiple measurements and average them, but it is a more manual process and much less sophisticated.
Dirac Live Calibration Tool does not require that you learn how to use any additional software. Everything is built into the tool. It provides a single solution for measuring and correcting both your speakers and your room. REW is a more hands-on tool, for those who like to learn and experiment.
Dirac Live is a proprietary algorithm that miniDSP licenses from Dirac Research. While the cost of the licensing is built into the price of each Dirac Live-capable hardware unit, it is a significant part of the cost. REW is completely free. We are very happy to be able to collaborate with both groups to offer different solutions to our customers.
A third option[Top]
While we are often asked the question about the differences between REW and Dirac Live, there is also a third option: our OpenDRC series of processors. These processors contains onboard IIR (crossover and parametric EQ) filters as well as banks of FIR filters. They are "open" because they simply accept the coefficients for the FIR filters, which must be produced by other (non-miniDSP) design software.
With this option, you have the full power of combined IIR and FIR filtering available - but you need to learn how to use it! Designing FIR filters is not straightforward, but there are a number of software programs available that you can use, both free and commercial. We have put together a list to help you get started at FIR Filter Tools.
That's it for this app note! Have fun, and regardless of which room correction solution you choose, please share your experience with other community members in our forum.