Introducing the world of Digital Room Correction (DRC), a process where digital filters are used to correct speaker + room aberrations. A 3 step process yet an acoustical challenge where DSP & Math Gurus use all resources to solve this complex problem. The following lines will summarize the basics of room correction in a setup involving a PC/Mac with a measurement/filter generation software, a measurement microphone and an audio processor (OpenDRC).
The first step in any Room correction process is to "listen" to the room + speaker interaction. Using a a software + measurement microphone combo, a set of test sweeping tones are played back through your speaker systems and recorded by the software application. No doubt that your neighbors will be wondering what you're up too! However please don't despair, because providing you do it well, it will lead to great results and they will be the envious one... Back to the technical aspect, the sweeps are used to "measure" the response in both time and frequency of your system. Since the resulting impulse response will be key to the filter generation (step2), this step is key to your success. Depending on the software used, you may have to take one or multiple measurements in different locations.
At the center stage of "good to great" room correction fitlering is the array of math and psycho-acoustic models used to "generate" filters based on the measurement. In audio, two types of filters are typically used: IIR (Infinite Impulse Response) or FIR (Finite Impulse Response). In today's realm, most room correction filters are either FIR based or a combination of FIR + IIR filters. While each software has a different interface and its ways to calculate the filters, a comon element is the"target curve". In other words, the expected frequency response and a guideline for the filter generation.
Your filter settings are now ready and it's time to listen to the end result. This is where the OpenDRC plays a key role. What used to be a noisy/power hungry PC running in the middle of your Hifi set is now a low cost, low power yet powerful processor thanks to the introduction of the OpenDRC units. With a range of all digital, all analog or hybrid, the OpenDRC is a solution for multiple configurations. It is a set and forget where the end user still get a chance to tweak some settings by allowing end users the flexibility they expect in today's world.
With the OpenDRC concept of becoming a leading open architecture FIR engine for room correction, a couple of software developers already came on boards to provide an array of Filter generation software. The following list is to be updated over time as software currently under development become available to our end users.
Based on Acourate technology from the well know Acourate audio package, AcourateDRC is a room correction only solution for computing filters compatible with OpenDRC platforms. The software has a simple user interface able to output .bin filters directly compatible with our platforms. For more information, please have a look at the following link.
A free command line tool and an Open Source project ported by Mason A. Green and based based on the work of Dr. Balázs Ban hosted at the following webpage. This package allows one to specify a target curve and generate the corresponding loudspeaker-room correction filters for the OpenDRC platforms. For more information, please have a look at the following link.
rePhase is a loudspeaker phase linearisation, EQ and filtering tool compatible with the OpenDRC-DI/AN and miniSHARC products. rePhase let you generate finite impulse responses (FIR) specifically tailored to reverse the phase shifts introduced by the crossovers of your loudspeakers (passive or active), resulting in a linear-phase system. It can also generate linear-phase EQ and crossover filters of arbitrary slopes, including Linkwitz-Riley (albeit linear-phase) and Horbach-Keele shapes.
You're ready to try the OpenDRC room correction experience and want to know what's required. Here are the basic core element for a stereo configuration:
And that will be it for you to be ready to go!