Dirac Live – More technical information
Using a look-ahead buffer makes it possible to perform impulse response correction
Minimum-phase and linear-phase room correction filters are physically incapable of optimizing the acoustic impulse response in a room. At best, they can minimize problems caused by filter application. Room-acoustic responses are typically 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 single zone.
Dirac Live utilizes a large number of measurement positions in the car, thus making it possible to accurately locate and correct acoustic problems.
This measurement data is then used to optimize the direct wave and early reflections in the time domain. Generally, there is less consistent time-domain behavior at higher frequencies. Dirac Live automatically identifies 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 car that causes spectral coloration. This is corrected in the frequency domain to achieve the perfect resolution.
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 various filter structures optimized for the problem and processor at hand.
Choosing a target response
A flat frequency response doesn’t sound neutral in a car due to the ratio between direct and reverberant sound and the frequency-variable propagation loss. Dirac Live can’t remove the late reflections, as they change too much between different positions, making a substantial roll-off necessary in a car. Dirac Live allows you to set your preferred target response with any amount of detail and adjust it during the tuning work.
Dirac Live 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:
- 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