Digital room correction
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Digital room correction (or DRC) is a process in the field of
History
The use of analog filters, such as
Operation
The configuration of a digital room correction system begins with measuring the impulse response of the room at a reference listening position, and sometimes at additional locations for each of the loudspeakers. Then, computer software is used to compute a FIR filter, which reverses the effects of the room and linear distortion in the loudspeakers. In low performance conditions, a few IIR peaking filters are used instead of FIR filters, which require convolution, a relatively computation-heavy operation. Finally, the calculated filter is loaded into a computer or other room correction device which applies the filter in real time. Because most room correction filters are acausal, there is some delay. Most DRC systems allow the operator to control the added delay through configurable parameters.
Implementation
The most widely used test signal is a swept sine wave, also called
Challenges
DRC systems are not normally used to create a perfect inversion of the room's response because a perfect correction would only be valid at the location where it was measured: a few millimeters away the arrival times from various reflections will differ and the inversion will be imperfect. The imperfectly corrected signal may end up sounding worse than the uncorrected signal because the acausal filters used in digital room correction may cause pre-echo. Room correction filter calculation systems instead favor a robust approach, and employ sophisticated processing to attempt to produce an inverse filter which will work over a usably large volume, and which avoid producing bad-sounding artifacts outside of that volume, at the expense of peak accuracy at the measurement location.
Software
Free software
Room EQ Wizard
Room EQ Wizard, or REW for short is a free room measurement tool with SPL, phase, distortion, RT60, clarity, decay, waterfall, and spectrogram views. REW also features IR windowing, and SPL meter, room simulation for subwoofer placement, and peaking filter-based EQ generation for multiple platforms, DSPs, and AVRs with a target curve editor.
Cavern QuickEQ
QuickEQ is part of Cavern, a free and
RePhase
RePhase is a free EQ and crossover generation tool that also linearizes phase response. RePhase has multiple configurable filter sets available for manual filter composition, which then can be exported as a single FIR impulse.
Commercial software
Most new AVRs include room correction in their setup, and a microphone in the box. Dirac Live is a commercial software that is available for PC and select Onkyo, Pioneer, Integra, StormAudio, and other AVRs. Denon and Marantz AVRs use Audyssey, and more expensive models allow for more corrections, and since the 2023 model year, Dirac Live as an alternative. Anthem AVRs use a proprietary software called Anthem Room Correction, or ARC for short, Yamaha uses Yamaha Parametric room Acoustic Optimizer (YPAO), as well as Trinnov Audio with their optimizer solution.
Industrial software
DCI-compliant hardware that are used in commercial theaters, sometimes use commercially available room correction software. Notable examples are IMAX cinemas, which use Audyssey MultEQ XT32,[2] while Datasat processors (found in all DTS:X rooms) have Dirac software. Dolby's CP850 and CP950 processors (which support Dolby Atmos) use a proprietary solution called AutoEQ. AutoEQ measures 5 to 8 microphone positions simultaneously. It requires loudspeaker specifications manually entered for the room. Earlier Dolby processors, such as the CP750, used a 31-band equailzer for the 5 or 7 main channels, and a single peaking filter for correcting the subwoofers' largest peak. The CP750 didn't have a swept sine wave generator, and used pink noise for measurement.
See also
- Deconvolution
- Digital filter
- Filter (signal processing)
- Filter design
- LARES
- Stereophonic sound
- Surround sound
References
- Michael Gerzon's paper on Digital Room Equalization, on audiosignal.co.uk.
External links
Open Source Implementations
Free Room Correction Software
Commercial Room Correction Software
- Acourate
- Audiolense
- Dirac Live
- Focus Fidelity
- HouseCurve
- IK Multimedia ARC System
- SoundID Reference from Sonarworks
- Trinnov Optimizer
Papers
- On Room Correction and Equalization of Sound Systems, by Dr. Mathias Johansson, Dirac Research AB
- Digital Room Equalization, by Michael Gerzon
- Audio Equalization with Fixed-Pole Parallel Filters: An Efficient Alternative to Complex Smoothing, by Balazs Bank
Articles
- Room Correction: A Primer, by Nyal Mellor of Acoustic Frontiers
- Sound Correction in the Frequency and Time Domain, by Bernt Ronningsbak of Audiolense
- The Three Acoustical Issues a Room Correction Product Can't Actually Correct, by Nyal Mellor of Acoustic Frontiers
References
- ^ "Focal Kanta measurements". Stereophile. Archived from the original on 2020-08-13. Retrieved 31 July 2021.
- ^ "IMAX + Audyssey". IMAX. Archived from the original on 2016-01-10. Retrieved 31 July 2021.