Dirac HD Sound – More technical information


Sound Improvement Instead of Sound Effects


Several types of sound effects have been used in TVs and other sound systems in order to correct sound imperfections. However, these one-size-fits-all sound effects treat the symptoms – not the cause – of acoustic imperfects, and often cause headaches or listening fatigue after extended use. Consequently, most consumers simply turn these effects off. 

Dirac HD Sound instead tackles the root of the problem by addressing the inherent physical limitations of the loudspeakers themselves, providing the most natural and pleasing audio enhancement solution. Once the offending acoustic anomalies have been addressed by Dirac HD Sound in the digital domain, there is simply no need for less sophisticated solutions. Simply put: Dirac HD Sound shines where general purpose solutions fall short.


Sound Quality First


Dirac HD Sound is a premium mixed-phase speaker correction technology. Unlike equalizers and other sound-correction systems, Dirac HD Sound also optimizes the sound system’s transient reproduction – a critical factor for accurate staging and clarity. Equally as useful for studio monitors as for earphones, TVs or entry-level docking stations, etc., the technology optimizes the sound reproduction as far as the laws of physics allow.


Multiple measurements


Dirac HD Sound obtains a correction using several acoustic measurements at different positions in an anechoic or semi-anechoic environment, taking into account how the sound field varies in space. Time-domain and frequency-domain corrections are computed from all of the measurements, not just an average impulse or frequency-response average, in order to optimize the entire sound field created by the audio system.

The Dirac HD Sound algorithm takes into account the variations between measurement positions in order to carefully tailor a correction that will work throughout the entire listening space. The trick is to correct as much as possible, but no more than exactly what is required: high resolution where it makes sense, and lower resolution where a detailed adjustment would be too sensitive to listening position.


Mixed-phase technology


  • Impulse response correction can only be obtained using mixed-phase filters
  • A look-ahead buffer makes it possible to perform impulse response correction, by mixed-phase filtering
  • Other attempts at loudspeaker correction employ minimum-phase or linear-phase filters, and thus fail to optimize impulse response.
  • Dirac HD Sound optimizes the impulse response and the magnitude response of the sound system, thus making it less sensitive to the challenges of room acoustic


Impulse response correction


A loudspeaker’s impulse response affects the clarity, detail and all spatial aspects of sound, such as location and distinctness. By focusing on consistent problems across the measurement positions and correcting only these, Dirac HD Sound is able to 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. As a result, power is delivered at just the right time, providing better punch along with more precise sound stage and imaging.


Frequency response correction


Conventional sound processing technologies employ only frequency in determining how to improve sound quality. However, a sound field is composed of several other dimensions, such as time and space. Most legacy technologies don’t employ any time-domain correction at all, and instead use minimum-phase or linear-phase filters with pre-determined time-domain characteristics. This causes smearing of the system’s response, and is a common reason why many of these solutions introduce new time-domain problems into the sound.

Dirac HD Sound is unique in that it treats a time-domain problem as such, and not as a minimum-phase spectral issue.


Implementation for best accuracy


  • Traditional EQ uses IIR filters for lowest processor usage
  •  Many loudspeaker correction filters use FIR filters for ease of optimization
  • A Dirac proprietary filter structure ensures maximum resolution with minimum processor usage


Flexibility and time savings


If you are a speaker designer, Dirac HD Sound is a tool that offers you increased flexibility that saves valuable R&D and engineering resources. Even tiny adjustments are done easily – without changing any hardware components – simply by adjusting the target frequency response curve on Dirac HD Sound’s graphical interface. With Dirac HD Sound, you can tailor the sound to your desired character, retaining full control of the time-domain.


Highly sophisticated, easy to use

We’ve specially developed the software for designing Dirac HD Sound filters for ease of use – but without compromising flexibility and performance. Measurements are made within only a few minutes , corrections can be limited to a certain frequency range and detailed changes can be played back immediately, giving you more time to focus on tailoring the target response to your liking. 


Further reading


Dirac HD Sound 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, Åhlén, 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.