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Digital Room Correction with Digital Signal Processor (DSP)

The Problem

Mother nature gave us a lot of gifts, but a perfect acoustic space wasn't one of them!

Put it simply, acoustic theories are very complex to analyze, model and unless your room was designed by a world famous acoustician, it will always be an uphill battle against the laws of phisics. While a certain amount of audio filtering; also called room correction can help to perfect the audio performance, achieving flat frequency response by boosting the signal at certain frequencies will only solve the issue if problems are not time dependant (see more below). Of course, quality of your loudspeakers, amplifiers and any other devices on the audio chain matters, but in the end acoustic theories trump. Following this little disclaimer, let's have a look at what DSP board can do for you.

Let’s take as an example the Hifi system of a living room illustrated in the below picture.

Many elements will affect quality of the audio system, such as:

•    The window that won’t absorb acoustic energy and will most likely reflect lots of high frequency energy from the left speaker
•    The imperfect free field frequency response of your loudspeaker system
•    The asymmetrical room layout which will affect the stereo field
•    Or simply the listener’s position by the sofa. So close to the back wall, he will most likely experience more low frequency than he should from the so-called standing waves. All together, the end result is an imperfect acoustic space where even the best Hifi audio system will hardly produce a flat frequency response.

How MiniDSP kits can help?

So besides taking down walls, moving your sofa around the room 5 times or considering changing the color of your speaker cable, there are few tricks which can help you improve the overall system performance. Digital audio processors like our MiniDSP Kit are one of them. Thanks to their configuration flexibility, they provide a low cost option to configure audio filters, equalizers and signal monitoring from a simple software interface. However note that there is a limit to how much digital signal processing can solve acoustic issues. In particular, equalization will only solve amplitude related issues.While room modes and other comb filtering (cancelations of waves) issues will require either time alignement or acoustic treatment.

What miniDSP can do, is provide you with a set of filters to easily improve the performance of your speaker system:
•    Graphic equalizer: This bank of filters will  increase or decrease the signal at a specific frequency. Depending of the MiniDSP firmware configuration, you may have 31 bands (also called 1/3 octave) or 15 bands (2/3 octave) available. By boosting/dampening the signal at certain frequencies, speaker equalization is the most common tool for system tuning
•    Parametric equalizer: Similar to the graphic equalizer, but this time with only a limited number of equalization bands that can easily be configured to better fit the needs of the application.
•    Delay: In order for loudspeakers to produce constructive wave front  and prevent as much comb-filtering effect as possible, time alignement of different loudspeaker are typically required. The delay blocks will also come handy in digital crossover applications.

So to summarize this application note, flat frequency response of a system will not happen by the magic of a DSP (no matter which brand it is). However, what our boards can do is help you improve the speaker equalization by boosting/dampening few specific frequencies your enclosure + driver combo may not be able to reproduce.

Our kits are also the perfect fit when it comes to digital crossovers. With their small form factor, one can easily place the board inside the enclosure of active loudspeakers. Hope this makes sense and send us an email if you have some comments to add.

About the Author

Tony is the co-founder of DSP4YOU and miniDSP, two companies dedicated to digital signal processing for audio applications. Besides his passion for audio, electronics and music, Tony loves traveling through out Asia Pacific, discovering one culture at a time what the world has to offer.

Robert Peston
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