Dirac Live – More technical information
What is the time-domain,
and why is it important?
At Dirac, we believe that the reproduction of transients is critical for a truly natural and transparent sound. For example, the stereo image is critically dependent on the time-domain differences and similarities between the sound at the left ear and the right ear. As such, Dirac’s impulse response correction improves the depth, the positioning and distinction of individual voices and instruments.
Mixed-phase room correction technology
Using a look-ahead buffer enables impulse response correction
Minimum-phase and linear-phase room correction filters can’t physically optimize the acoustic impulse response in a room. At best, they can minimize problems caused by the application of a filter. Room-acoustic responses are non-minimum-phase, which is why Dirac Live uses mixed-phase correction.
Dirac Live is unique in that it improves the impulse response throughout the listening area, not just in a particular zone.
Dirac Live uses several measurement positions (typically 9) in the listening room, making it possible to accurately locate and correct acoustic problems.
In terms of the impulse response, this means optimization of the direct wave and very early reflections. Generally, at higher frequencies there is less consistent time-domain behavior. Dirac Live room correction automatically finds consistent problems in a frequency-dependent way and corrects for them. After addressing consistent time-domain behavior, there may still be some late reverberation in the room that causes subtle coloration. Dirac Live corrects these in the frequency domain to achieve just the right resolution.
Impulse response correction
A loudspeaker’s impulse response affects clarity, detail and all spatial aspects of the sound. Dirac Live is unique in that it actually corrects the impulse response throughout the listening area, not just at a single point. By focusing on consistent problems across the measurement positions and correcting only these anomalies, Dirac Live can achieve a faster decay time. Typically, the power ratio between the direct wave and the tail (later-arriving echoes) is improved by 6 dB or more, representing a vastly improved overall sound.
Frequency response correction
Why is it that the same frequency response can sound so different from room to room? The answer lies to a large extent in the time-domain aspects of the measured frequency response, as well as critical differences in the spatial (angular) domain. By addressing time-domain problems as such, and not as minimum-phase spectral problems, frequency response correction becomes more effective. After having conducted time-domain correction, we then treat the spectral colorations in a room. By paying particular attention to the variations across different measurement positions – not just the average – we can make sure not to overcompensate.
Implementation for best accuracy
Traditional EQ uses IIR filters for lowest processor usage
Many room correction filters use FIR filters for ease of implementation and optimization
IIR and FIR filters both have their pros and cons. At Dirac we use a proprietary filter structure that achieves maximum performance at much less processor usage than regular FIR filters. This filter structure also has great numerical properties, and thus doesn’t produce any digital noise.
Choosing a target response
A flat frequency response does not necessarily sound neutral due to the ratio between direct and reverberant sound and the frequency-variable propagation loss. Dirac Live can’t remove late reflections, because they change too much between different positions. Therefore, a slight roll-off is often appropriate when listening at a distance. The Dirac Live algorithm suggests a target response appropriate for your listening environment and speakers, which you can of course adjust to your taste using our simple graphical interface.
Advanced, yet very simple to use
You don’t have to be a signal processing or computer expert to enjoy the benefits of Dirac Live. All of the Dirac technologies that comprise our world class digital room correction solution are automatically managed by our software, making it easy for users of all kinds. All you to do is position the microphone and press “Play” – our software wizard will take care of the rest. Advanced users are free to edit the target response as desired using a simple graphical interface. Otherwise, just press “Optimize” for the most lifelike reproduction of your favourite music!
Dirac Live digital room correction technology is used in the most demanding environments – a credit to our vast body of knowledge built up through R&D over decades. While a complete list of patents and publications is extensive, you can find a few key references below:
- Dirac Room Correction, Brännmark, Audio Engineering Society, AES, Sweden lecture Nov 2014.
- Spatially Robust Audio Compensation Based on SIMO Feedforward Control, Brännmark, Ahlén, IEEE Trans Signal Processing, May 2009.
- On Room Correction and Equalization of Sound Systems, Johansson, invited talk at panel discussion on “FIR or IIR? That is the question!”, 123rd AES Convention, NY, USA, 2007.
- Room Correction and Equalization of Cinema Sound Systems, Johansson, invited talk at ICTA Annual Seminar, LA, USA, 2010.