Or do we cherry-pick which recordings get treated by inserting an equalizer somewhere in the signal path? This last option has been the least appealing to many audiophiles, due to the undesireable sonic side effects that can result while trying to "fix" a bad recording. For example, you may increase the bottom end or take some glare out of the midrange, but now the soundstage is smeared and flattened.
But what if you could have your sonic cake and eat it too? That's what DEQX says it can offer with the official launch of its PDC-2.6P two-channel preamp. Based on its PDC-2.6 speaker and room correction processor, the new preamp features a remote-control analog volume control and 100 memory digital parametric equalization for selectively correcting recordings.
According to DEQX, the analog volume control follows 12MHz DACs to maintain "full audio resolution" at low listening levels. The included remote also can provide control of minimum phase equalization with high and low shelving and a variable parametric band that can be centered at any frequency in semitone increments. Bandwidth is adjustable from a single semitone to four octaves, and there are four sets of stereo inputs: unbalanced (RCA), balanced (XLR), digital AES/EBU (XLR), and digital S/PDIF (RCA).
But why is this equalizer any better than its predecessors? DEQX's Kim Ryrie states, "DEQX Calibrated correction provides amplitude and phase correction of the full audio spectrum—especially in the mid to high frequencies—with minimal latency. If you can imagine a graphic equalizer that had about 4000 bands that actually corrected phase at all frequencies rather than making it worse, you've got an idea how different DEQX is to traditional analog and digital EQ."
DEQX says that both PDC models also provide phase and delay-corrected crossovers for subwoofers or up to three-way active speaker designs, using linear phase crossovers and phase correction technology (the six analog outputs from the PDC allow two-way or three-way linear phase digital crossovers with slopes up to 300dB/octave). In addition, the DEQX PDC units provide both speaker and room correction, using near-field measurements for speaker correction, and listening position measurements for room correction, based on a combination of FIR (Finite Impulse Response) and IIR (Infinite Impulse Response) filters.
Ryrie adds, "DEQX Calibrated processing can provide a perfectly flat near-field frequency response with correspondingly corrected phase response. For room correction however a flat room response is not desirable because mid to high frequencies are increasingly absorbed by the room and distance as pitch increases. This typically results in a 6 to 8dB fall off by 20kHz at the listening position compared to, say, A440 in a reasonably dampened room. We recommend that simple room dampening be applied to the walls and floor, so that a corrected speaker sounds natural, and that room correction only be applied electronically at the lower frequencies—typically below 300Hz."
According to Ryrie, "The PDC-2.6 and PDC-2.6P offer the most comprehensive audio measurement and correction processing available for professionals and serious consumer audio users. DEQX Calibrated processing addresses the fundamental problems of speaker design and room acoustics that simply cannot be dealt with using analog technology."
Pricing for the standard configuration DEQX Calibrated PDC-2.6P preamp is approximately $3500 in the US. DEQX has also recently announced a co-development deal with loudspeaker manufacturer NHT.