November 2000Perpetual Technologies P-1A Digital Correction Engine and P-3A Digital-to-Analog Converter
by Doug Blackburn
Theyre baaaack. Mark Schifter and Peter Madnick of Audio Alchemy, that is. They're now in the thick of it with Perpetual Technologies, which has been demonstrating engineering models and prototypes of their P-3A DAC and P-1A DSP engine at major audio shows for a while, always to appreciative audiences. When the twins birthday finally arrived, Mark Schifter anxiously shipped a P-1A/P-3A pair to me while the units were still toasty warm. Because of the nature of these products, this review may chew up a few bytes, so lets not waste any CPU cycles getting on with it.
The P-3AThe $699 P-3A DAC is presented in a very small box, 5.5"W x 8.25"D x 1.75"H, with a sculpted silver aluminum front panel and an attractive gray speckle finish. One reason the box can be so small is the external power supply -- a wall-wart type with a small connector that plugs into the back of the P-3A. Perpetual Technologies claims -140dB THD+noise under optimal operating and measurement conditions. The dynamic range is 120dB, about as good as consumer audio product gets, even very expensive ones. In fact, most digital products have a dynamic range between 96dB and 114dB (higher numbers are better, and each 6dB means a 50% reduction in noise).
The P-3A can be placed in a vertical orientation using the aluminum feet supplied. Expose the adhesive on the double sided foam tape and stick the two feet on one side of the P-3A and it will stand up. Perpetual Technologies also provides four small adhesive-backed bumper feet to allow the P-3A to be laid down flat on a shelf. You can select the orientation to fit your space.The P-3A's digital inputs are: I-squared-S mini-DIN, AES/EBU, coax RCA, TosLink optical. Analog outputs are RCA only. Digital sources can output 16 to 24 bits and the P-3A can handle them; input sample rates accepted range from 8kHz-108kHz, with 192kHz optional through I-squared-S input.
Peter Madnick clarifies the operation of the P-3A and other so-called 24/96 DACs and 24/96 outboard processors this way: The P-3A does not interpolate 16-20-bit data to 24-bit data -- nor does any 24/96 DAC (e.g., the Bel Canto DAC1) or add-on 24/96 external device (e.g., Assemblage D2D-1). All of these products, so far, will output 24-bit data via dithering of the 16-bit input data. This results in data that has roughly 17 bits of equivalent resolution within a 24-bit datastream. The P-3A and other 24/96 products do upsample, for example, from 44.1kHz to 96kHz if you select that mode. People tend to assume that 24/96 products that advertise upsampling and/or interpolation actually convert 16/44.1 data to full 24/96 resolution, which is not accurate. To actually get 24-bit data in a 24-bit datastream, you must use digital signal processing (DSP), which is included in the P-1A and is referred to as "Resolution Enhancement" in the P-1A's user manual.
The P-3A's optional 192kHz mode requires a factory mod and doesnt have any consumer-product support at this time. But it could be a useful extra feature for people who are delving into 192kHz professionally or on the serious amateur level.
The front panel has two switches for mode setting, each with several LEDs showing the active selection. The "Input" switch selects the active input since there is no auto-sensing of this. The "Program" switch selects "normal" or "reversed" polarity of the analog output signal. Additional LEDs indicate the sampling rate, which is normally 96kHz. Unless you have a photographic memory, you'll need the owner's manual to decode which LED means what since they are labeled 1 to 3 and 1 to 4 rather than having text labels.
In the same size small box as the P-3A, Perpetual Technologies has squeezed a miracle of modern audio design. The $950 P-1A is a digital signal processor -- Perpetual Technologies calls it a digital correction engine. It can upsample any input frequency to 96kHz, it can interpolate any input data to 24 bits, and it is claimed to reduce jitter to vanishingly low levels.
The P-1A's digital inputs are I-squared-S mini-DIN, AES/EBU, and coaxial RCA, and the digital outputs are identical. The P-1A can accept incoming information in 16- to 24-bit formats at sampling rates from 8kHz to 108kHz (192kHz is optional through I-squared-S input). Output bit resolution is user selectable and includes settings for 16, 18, 20, and 24 bits. The output sampling rate is also user selectable at 44.1kHz, 48kHz, 96kHz, and optional 192kHz through I-squared-S output. Perpetual Technologies recommends using the supplied I-squared-S cable when lashing the P-1A and P-3A together, and I agree. Even though the supplied I-squared-S cable looks like it cost maybe $1 in large quantities, it sounded better than my reference digital coax cable, which costs more than $250. Higher-quality I-squared-S cables are supposed to be in the works.
There is also a USB port on the back of the P-1A. You can purchase special software from Perpetual Technologies, load it on your PC, and you can then download new software for the P-1A via this USB port. Two extra-cost software-based correction products have been announced: loudspeaker correction priced at $399 and room correction priced at $699. Neither is available at this time, but Perpetual Technologies has demoed speaker correction. We will investigate both at a later date, but here are a few details.
Many loudspeaker manufacturers have provided Perpetual Technologies with performance parameters of their loudspeakers. From those parameters, Schifter, Madnick and crew generate generic correction files. If you modified your speakers so that they are not stock any longer, or if you built your own speakers or if your speaker manufacturer is no longer in business, Perpetual Technologies is working on an extra-cost process that will involve sending you a measurement device. You measure your speakers and return the device to Perpetual Technologies; they then create a custom correction file for your speakers.
Obviously, there is no such thing as generic room correction because every room is different, so all room correction will require actual in-room measurements. If you change anything in the room -- draperies, speakers, equipment locations, etc. -- the correction file will no longer be valid, and youll need to re-measure and get new compensation files created.
When used with the P-3A, you set the P-1A to interpolate to 24 bits, but you leave the sample rate the same as the input. Set this way, the P-1A will output 16/44.1 CD data as 24/44.1. The P-3A will then upsample from 44.1 to 96kHz. Early-on I had inadvertently set the P-1A to upsample to 96kHz, and the P-3A to upsample to 96kHz. It wasnt too long before I was trading e-mail with Perpetual Technologies wondering why the pair did not sound as good as I was expecting them to sound. Once we figured out what was going on, I reset the P-1A and things improved significantly. So let that be a lesson -- upsample one time good, upsample two times bad!
Because of the potential the P-1A has, it should be looked at somewhat differently than other components. But we cant review "potential" so this review will only cover the P-1A used as a front end for the P-3A. In that mode, all it is doing is interpolating data to 24 bits (from the 16-bit CDs fed it) and reducing jitter to a claimed 2 picosecond specification, the same incredibly low number claimed by Assemblage for the D2D-1 jitter reducer and upsampler/interpolator.
The front panel of the P-1A has two push-button switches, each with several LEDs to indicate status of settings. There are four functions you set with these two switches -- and this produces a significant annoyance for me. The mode (enhancement or no enhancement) and active input are visible all the times. The output bits and output sampling rate are "hidden" and can only be checked or set by pressing both front-panel buttons. Early in the review cycle, while unfamiliar with this user interface, I made incorrect settings a couple of times before I realized my error. Owners would be much better served if the front panel had four switches and four sets of LEDs. The LEDs on the front panel now are labeled 1 through 3 and 1 through 4, and it's difficult to remember which LED means what without referring to the user's manual. Separate switches and LEDs would permit logical labeling and would do away with the necessity to have to keep the manual handy constantly when you are changing equipment or sources.
A note on power
The P-1A and P-3A do not use identical power supplies. The voltages supplied to each product are different -- 9 volts AC to the P-3A and 12 volts DC to the P-1A. However, the power connectors on the backs of the P-1A and P-3A are identical. This means you could inadvertently connect the wrong power supply. Im not sure if this would damage either device, but it should not be able to happen. At the very least, there should be a label on the end of each power cord that identifies the plug as being for the P-1A or P-3A. At best, the connectors should be different shapes, so no connection error could be made. The situation that exists today is without doubt a result of using off-the-shelf power supplies. Perhaps custom terminations will be possible in the future.
Used on its own, the P-3A reminded me, to a startling degree, of the sound of the stock Assemblage DAC 2.6, which also sells for $699. Both are transparent and dynamic, with a large soundstage, but they're a bit lean harmonically and lacking some of that indefinable characteristic that compels you to want to listen to music in every spare moment. The sound isn't bad -- it just doesn't keep drawing me back to listen to music repeatedly. The P-3A makes female vocal sibilants a bit too obvious and distracting -- a characteristic I seem to find more problematic than many other listeners who apparently tolerate that sort of thing as if it were perfectly OK. The DAC 2.6 and MSB Link DAC both have more natural sound on sibilants. The P-3A also gives some recordings a small upper midrange/lower treble push -- a very small emphasis, but audible and consistent on recordings with the right spectral content. The DAC 2.6 had a more neutral presentation with the same recordings, while the MSB Link DAC is a bit reticent in the same frequency band. The P-3A's soundstaging was a match for the DAC 2.6's and considerably more precise than that of the Link DAC. The P-3A offers a large, deep soundstage thats comparable to the best of its competitors.
I should remind you that the best DACs in the $700 price category today are far better than digital front-ends of even two years ago, including some costing ten times as much. People used to the sound of two-year-old or older DACs will go absolutely nuts over the P-3A's sound. Comparisons to past and present DACs are important for understanding just where the P-3A is in the sonic pantheon circa fall 2000.
MSBs Link DAC ($399) powered by MSBs P1000 Power Supply ($299) is an interesting contrast. The MSB lacks upsampling and interpolating capability. This appears as a grayer, less transparent sound and points up the superior transparency and dynamics of the P-3A. Yet the Link/P1000 combination is harmonically rich and lush-sounding in a way the P-3A cannot match. The Link/P1000 combo has more sustain and echo to go along with the richer harmonics. The P-3As bass is clearly under better control and lower in distortion. A friend who was experiencing the stock $400 MSB Link III for the first time (with a DVD player as a transport) was quite complimentary of the sound. So maybe Im just ultra picky and sensitive because of all the DACs I've been hearing lately. Compared to the analog outputs of just about any stock DVD player, regardless of price, the P-3A is a sonic revelation. I found the stock DAC 2.6 perfectly OK-sounding but uncompelling, while the fully upgraded version, for about $300 more, was highly compelling and much more musically satisfying.
P-3A, allow me to introduce you to the P-1A
Well shuck my jive! Can this be the same DAC I just wrote about? Let me look again just to be sure. Yup, its the P-3A all right. OK, adding a $950 DSP engine onto a $700 DAC ought to do something pretty special; otherwise why bother? The sonics are elevated to a much more enjoyable level. You know the list -- soundstaging, imaging, bass quality, transparency, detail, et al. The improvements are very significant and unmistakable. Every CD, any CD, rides the escalator to more refined sound.
The Assemblage D2D-1 reduces jitter to the same claimed levels as the P-1A/P-3A combo, upsamples from 44.1kHz to 96kHz, and dithers (called "interpolation" by Assemblage) 16-bit data within a 24-bit datastream, yet its effect when used with the Assemblage DAC 2.6 or DAC 3.0 is not as great as the effect of the P-1A on the P-3A. That doesnt mean the two Assemblage pairings dont sound as good as the Perpetual Technologies duo. The DAC 2.6 with all upgrades plus D2D-1 (about $1750) is stiff competition for the P-1A/P-3A. Both pairings are very transparent, dynamic, detailed and have a large enveloping soundstage. Id place the P-1A/P-3A duo slightly ahead in transparency and detail, while the DAC 2.6/D2D-1 has the edge in bass slam and neutrality. The Assemblage DAC 3.0 with upgrades paired with the D2D-1, approximately $2700, is clearly better, with an edge in transparency, refinement, detail, soundstage size, image sharpness, bass control and power, complete neutrality, and a compelling musical presence that puts it right up there with the best digital sound at any price.
The only specific criticism of the P-1A/P-3A duo is that the pesky upper-midrange/lower treble emphasis can still be heard from time to time with the right musical content. Its reduced significantly from the P-3A by itself. If Id not heard those recordings on other digital front-ends without that extra bit of upper-midrange/lower-treble energy, Id be inclined to blame the recordings, but thats not the case. The degree of this sonic character, however, should not be misunderstood. It's not huge and may not even be noticeable to many listeners. But it's my job -- to notice and report.
The P-1A/P-3A combo does a lot for $1650. And, in fact, it may just be as good as it gets at this price point. I mention this only to place the P-1A/P-3A duo in the digital front-end pantheon as accurately as I can. The P-1A/P-3A will get you into the big leagues, but to go toe-to-toe with the best of the best, you need a slightly sharper implement.
Adding the Monolithic Sound P3 power supply
For this review I was also able to use the $349 Monolithic P3 Perpetual Power Plant Power Supply, a beefy dual power supply in a box the size of a large brick. Connect a conventional power cord to AC power and connect the two supplied umbilicals to the P-1A and P-3A. Yep, thats right -- one power supply for both Perpetual Technologies boxes. Monolithic runs into the same rut Perpetual Technologies runs into -- two identical umbilicals and no identification on the cable as to which goes where to help the owner make error-free connections. Labels would have been a nice touch. The simple front panel has only a power LED. The rear panel has the power outputs for the P-1A and P-3A, a resetable circuit breaker, and an IEC socket for the power cord. The Monolithic P3 Power Supply has no big surprises. There is an input filter, separate transformers for each power supply, rectification, and filtering -- solid, common-sense analog-power-supply design.
The difference in "content" between the Monolithic P3 Power Supply and the low-cost power supplies provided by Perpetual Technologies is night and day. Yes indeedy. For those willing to extend their commitment by another $349, the one-box, two-output Monolithic P3 Power Supply for the Perpetual Technologies duo nicely elevates the sonics of the P-1A/P-3A, closing about two-thirds of the performance gap to the upgraded DAC 3.0 and D2D-1 combo. This is heady performance indeed, right at the threshold of "it doesnt get any better than this."
The sound improves in expected ways. Most immediately noticeable is the reduced background haze. Next you begin to notice that detail, dynamics and image sharpness have become harrowingly natural -- youd swear you could reach out and touch the instruments, if not the musicians. When the bass kicks in, it really kicks in -- with authority and drive the stock power supplies cant muster, decent though they may be. Youd swear the transparency was so good you could hear your breath condensing in 40-degree air. I felt a distinct through-the-looking-glass character to the music when using the P3 power supply -- as if I walked into the music venue. I was more of an outside observer with the stock power supplies.
The pesky occasional upper-midrange/lower treble emphasis remained audible though. It is reduced in level for a second time, now getting pretty hard to detect, just barely there -- and again only on certain recordings. If you press me to quantify the recordings that produce the audible effect in my system, Id have to say about one-third of the CDs I listened to. In every other respect, the P-1A/P-3A/Monolithic trio is right up there with the very best digital front-ends. The Monolithic power supply pushes the P-1A/P-3A over a musical precipice, allowing you to get lost in the music to an extraordinary degree -- the highest expectation and greatest pleasure one can expect from any digital front-end.
This review was one of most complex and demanding I've written. Describe the performance of a roughly $2000 digital front-end, including Monolithic P3 Power Supply, as being very close to performing with the best of the best regardless of price is not something done without careful consideration. The P-3A DAC alone is competitive with other DACs in its price range, but it does not hint at what is possible sonically when the P-1A is added. The P-1A/P-3A combination synergizes remarkably and produces some extraordinary sound -- with only a slight upper-midrange/lower-treble emphasis on certain recordings to criticize. Adding the Monolithic P3 Power Supply further extends the high-end performance, putting the three-piece front-end shoulder to shoulder with the best of the best in many ways.
You may have thought that DAC performance had peaked out with the appearance of 24/96 upsampling and interpolation products, but the Perpetual Technologies P-1A/P-3A prove that progress is possible by not doing what everybody else is doing. Perpetual Technologies' decision to include new and innovative product capabilities like speaker and room correction extends the performance envelope of digital audio beyond conventional products. Consumers and manufacturers will now have to re-think digital audio completely. Are conventional digital products enough when something like the P-1A digital correction engine exists for under $1000?
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