Since studios have been moving into less acoustic-friendly spaces (e.g. spare bedrooms that quite frankly have no business hosting a music production system), the need for some means of compensating for poor acoustics has materialized. Studio monitor manufacturers have responded by developing various types of room correction technology. At the most basic level, room correction analyzes the frequency response of a room/loudspeaker combination and produces compensatory equalization.
How It Works
A test signal is played through the loudspeakers and captured using a measurement microphone, preferably placed at the mix position. The room correction system analyzes the loudspeaker/room response, compares it to the known response of the speakers and the measurement microphone, and then applies equalization to correct for the deficiencies of the acoustic space. This is not far off from the concept of shooting a room with pink noise, analyzing the results with a real-time spectrum analyzer (RTA) and applying inverse EQ, with say, a 31-band graphic.
Of course, the possibility that the average Joe owns (and understands how to use) an RTA are slim, so loudspeaker manufacturers such as Dynaudio Acoustics, Genelec and JBL started building studio monitors incorporating active electronics and on-board DSP with the ability to play a test signal (either noise or a series of blips and bleeps) and automate this process so that user error can be avoided. In some cases, the results can be a startling improvement over the uncorrected response of the speaker.
At least two audio manufacturers are marketing real-time room correction systems designed to work with any loudspeaker system. ARC from IK Multimedia runs real-time software in the form of a DAW plug-in to correct room response. ARC gets “plugged in” on the master L/R bus of say, a Pro Tools session, working in real time to correct changes in the room response. If you are mixing a song and an entire band steps into the control room and squeezes into the mix position, ARC recognizes the fact that the high-frequency response in the listening area has changed and compensates.
What Is CONEQ
CONEQ (CONvolution Equalization) from Real Sound Lab is a correction technology that can be employed in sound reinforcement systems to apply real-time room correction based upon the acoustic power frequency response of an audio system. Traditional acoustic measurement systems analyze sound pressure level (SPL) of sound waves at specific frequencies. So, if the system recognizes a 4.5 dB peak in the response at 3.15 kHz, a complementary cut is applied at the same frequency. The issue here is that an SPL measurement is made at a single point in space. CONEQ analyzes the sound field produced by the loudspeaker rather than the response at a specific point. In a process that takes only several minutes, CONEQ measures hundreds of points in a listening area, integrates these measurement points into a composite response plot using a proprietary algorithm, creates a high-resolution, inverse-response correction curve, and applies that curve to the speaker or speaker array to flatten its response.
The CONEQ measurement process is facilitated using CONEQ WORKSHOP software, run on any PC. The software provides a rapidly repeating swept-sine wave for the test signal. This signal is generated from your computer’s sound card and sent to the audio system. While it is being played, the microphone is slowly moved through the coverage pattern of the speaker and the software acquires measurement data at several hundred physical points. Real Sound Lab has a list of recommended sound cards and microphones so that measurements may be taken accurately, and sample rates may be user-defined to comply with the capabilities of the sound card.
Measurable Results
After the measurement process has been completed, CONEQ WORKSHOP software interprets the data and creates a 4,096-point correction filter as well as a graph depicting the acoustic power frequency response of the loudspeaker. Resolution of the correction curve may be increased or decreased to fit user needs, and multiple measurement sequences can be combined to balance the spectral response of left, right, center, surround and even delay fill loudspeakers.
Though a PC is always required to run CONEQ WORKSHOP for the measurement process and to generate the correction curve, this mega-filter set can be applied to the audio system in two ways depending upon the application. In the case of a PC-based recording/playback system, an engineer would use the software-based CONEQ P1 Equalizer or A1 Equalizer. When used with a traditional PA system that may not incorporate a PC, the data gathered in the measurement process is uploaded to non-volatile memory onboard the CONEQ APEQ-2PRO, a two-channel hardware box that hosts the CONEQ correction process and allows it to be applied to any sound reinforcement system.
Some of the benefits claimed by Real Sound Lab when using CONEQ include increased sonic realism and improved intelligibility, with a reduction in feedback — and indeed their demonstrations support these claims. In addition to CONEQ’s basic algorithm (intended to create flat response), the system may be used to target specific curves. For example, CONEQ could flatten the response of a computer’s sound card to improve measurement accuracy, compensate for deviations in the measurement microphone itself, or apply a preferred “house” EQ curve. It could possibly be used to make one type of loudspeaker sound nearly indistinguishable from another. Hmmm…
Steve “Woody” La Cerra is once again out on tour this summer mixing front-of-house for Blue Öyster Cult. He can be reached via email at Woody@fohonline.com.
