How to do Audio Room Correction with DSPs
Do you love great sounding audio?
Are you motivated to take full control of the audio in your home or office?
Then read on to learn how to bring great audio to your home, at affordable price and have some fun along the way by learning audio engineering. In just three steps you can create perfect sound.
- Measure your speaker and room interaction using miniDSP UMIK-1 calibrated microphone
- Decide on the audio response you want for your room
- Configure the miniDSP 2x4 (HD) with filter parameters
Here is a great video on how to use Room EQ Wizard (REW), a free software application you can use to generate the filters to apply the miniDSP so you can achieve room correction. If you have budget for a ~$325 DIRAC Live license, then the process is simplified. The following blog describes how you can use DIRAC Live along with miniDSP to achieve room correction. Let's learn more.
Digital Room Correction (DRC) is 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 (AcourateDRC) or multiple measurements (Dirac Live DDRC series) in different locations.
Step2: Filter generation
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.
Step3: Filter processing
Your filter settings are now ready and it's time to listen to the end result. This is where the miniDSP 2x4 HD 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 miniDSP's room correction units. 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.
Powered by miniDSP room correction units
With miniDSP's 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.
Introducing the Dirac Series of 24/96 high-resolution audio processors. miniDSP and Dirac Research bring you this unique hardware/software combination featuring Dirac Live® — the world's premiere digital room correction solution. For more information, please have a look at the following link.
- Python Open Room Correction (PORC)
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.
How to get started ?
You're ready to try miniDSP's room correction experience and want to know what's required. Here are the basic core element for a stereo configuration:
- 1 x miniDSP for audio processing of the stereo signal. This device will be located between the audio source and your speaker amplifier. Note that if you intend to use Dirac live, you must be sure to select a miniDSP device that is compatible.
- 1 x Measurement microphone such as miniDSP UMIK-1.
- 1 x A compatible software for calculation of the FIR filter parameters (E.g. Porc, rePhase, DRC FIR open source or your own software)
And that will be it for you to be ready to go!