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  dCS Delius and Purcell Sampling Rate Converters

      Date posted: November 23, 2000

dCS Converter

Sugg. Retail: $9900 CDN (Delius)
$6999 CDN (Purcell)
Distributor: Audiopathic
10692 Yonge Street,
Richmond Hill, Ont.
(905) 886-7810
FAX (905) 886-6920
www.audiopathic.com

(Reprinted from the Audio Ideas Guide A/V Almanac 2001)

      I’ve never thought of Purcell and Delius as particularly compatible composers, the former known for his sprightly baroque theatre and ballet pieces, and the latter for writing dreamy romantic tone poems with poetic titles. However, technology can bring anyone of any time together, and dCS has done so, making them work together like Britten and Pears.

      The Delius and Purcell do a few numbers together, too, specifically 192 kHz and 24 bits: the latter is a sampling rate converter (see our last issue’s look at the Assemblage SRC and DAC and MSB 96K DAC), which takes any digital signal and either up- or down-converts it, while also altering the bit rate up or down. Most commonly, these processes will be of the up variety to take a 44.1-kHz/16-bit signal up to 96/24, or even 192/24, in the process able to introduce noise shaping and dither to further refine the greater number of stairstep transitions in the digital signal.

      Both units will also do a large number of different digital operations too numerous to list here; it takes a full page to list the options for each, and most are esoteric functions that will generally be set once and left. For example, noise shaping can be set to 4 values, but that most likely to be used is Auto, which adjusts it to work best with each bit and sampling rate. These components are pretty much as complicated as you want to make them, the dCS engineers having set them up to work properly by default.

      Though both upsampling and downsampling are possible, the latter is pretty much a professional use for getting the highest resolution from 96/24 or 192/24 recordings onto CD, while the former is a way of accomplishing sheer digital magic. Theoretically, you can’t fully put Humpty Digital back together again, once his shell has been sampled into shards. However, with the power of prediction (noise shaping) and smoothing (dither), resolution can be improved, provided the signal is reclocked to a higher sample rate, and the number of bits is increased. The dCS engineers did not realize until the late 90s how effective this process could become in practice.

      Those skeptical about how the sound can be improved through all this are invited to read the aforementioned Assemblage/MSB reviews, where an extensive discussion of the technology is provided. However, I should note that real sonic improvements are definitely provided by moving the anti-aliasing filter in a DAC well out of the audio band; since this filtering is at half the sampling rate, it occurs at 48 kHz in a 96-kHz DAC, and at 96 kHz in a 192-kHz DAC. This completely eliminates any phase error, time smear, and other audible artifacts of this filtering process.

      The Purcell performs the appropriate sampling-rate changes after recognizing the incoming digital signal, be it 32, 44.1, 48, 88.2, or 96 kHz, and will output any of these, as well as 192 kHz. The Delius accepts the output of the Purcell, most likely 192 kHz in consumer use, and decodes it, outputting itself an analog balanced or unbalanced signal. Both units have extensive input and output flexibility (in the case of the all- digital Purcell), handling coaxial (BNC, RCA), optical (ST, optional, Toslink in on Purcell only), and AES/EBU.

      In our case, the transport was a Pioneer PDR-05 CD recorder, which has shown superb tracking ability and data integrity as a playback transport, via a Meridian coaxial digital cable, while the connection between the digital components was via a matched pair of Apogee Wydeye AES/EBU cables. Why a pair? The data format set up by dCS for 192 kHz divides the digital signal into the two stereo channels to eliminate possible crosstalk and to make the high-speed data signal easier to handle without error. As an aside, I’m sure that there are new owners of these dCS components who initially wondered why they got only mono from the Purcell/Delius duo until they more thoroughly explored the owner’s manual.

      About $17,000 may seem pretty expensive for digital signal processing until you examine some of the other capabilities of this pair, which constitute a digital preamplifier with inputs for all digital sampling rates (with DSD otional), with full level control. If all your inputs are digital, all you need is a power amplifier and speakers. Such a device as the Meridian 607 A/D converter could be added to accommodate analog inputs. Those not buying the notion of upsampling quite yet could build a system around just the Delius, which is on its own a full-fledged digital preamplifier that will handle all digital signals up to 192 kHz. Which begs the question, why bother with the Purcell at all?

      Well, the sound quality of the Delius is as good as it gets with the best sources. I heard this from its professional cousin, the 952 when recording The Bellingham Sessions in 1998, as we recorded at 96 and 192 kHz onto Nagra D recorders. The improvement from 96 to 192 kHz was as dramatic as that from 48 to 96, heard easily by all the musicians and observers.

      But most of what consumers listen to is CDs, like our resulting ones, which came from DAT tapes encoded with the Meridian 607. At that time editing 96/24 or (especially) 192/24 tapes was impossible, and upsampling not much more than a glint in a dCS engineer’s eye.

      But now that it’s here, and now that we all have large collections of CDs going back 15 years, the reason for adding upsampling is compelling, especially once you’ve heard what it does. Consistently I’ve heard more power and presence in the midrange, more air, detail, and ambience in the upper frequencies, and greater solidity, power and extension in the bass. There’s just more more there, to shamelessly steal a phrase from another reviewer without attribution (I can’t remember who it was)

      The difference between upsampled 96 kHz and 192 was subtler than the “real thing” comparison when recording, the major improvement heard going from 44.1 to 96. Unfortunately, I didn’t have all the toys at hand to upsample 96 kHz audio DVDs in the short period I had with the dCS composers (they are very much in demand, even at the premium prices, so distributor Angie Lisi could let me play with them for only the Labour Day weekend), but the inference is obvious: there would be an improvement, but I suspect it would be more subtle, since we’ve already got the ant- aliasing filtering out of the audio band to start.

      What surprised me in listening to a variety of CDs was that the greatest sonic improvement seemed to come from the oldest discs recorded with the earlier, cruder digital systems like Sony F1s. This was demonstrated especially by a 1983 Nimbus Ambisonic disc, Edward Elgar: Works For String Orchestra with the English String Orchestra conducted by William Boughton. I suppose I could say that we were adding the Elgar to the Purcell and Delius, if only as symbolic software.

      On Sospiri, which adds pedal organ to the strings, a distinct opening up of the soundstage could be heard, especially when played through our Cantares SSP-1 surround processor in UHJ Ambisonic mode. The surround image just seemed to get sorted out, increasing the realism of the sound and the enveloping nature of the Great Hall of the University of Birmingham.

     There’s also a pedal bass note at the end of Sospiri that will stress most subwoofers (I think at about 20 Hz; my Audio Control 1/3 octave RTA only goes to 25 Hz) that comes through with incredible presence. It even made the big Sunfire Signature sub dance, until I put larger, more absorbent rubber feet under it. Also notable was the sweetening of the string sound when upsampled, the recording previously sounding a little grainy and edgy. Why? Well, I think the older recordings have more phase error from recording anti-aliasing filters built into them, and much of that time domain distortion compounds with the filters in most CD players and DACs. Getting the filters out of the audio band in playback eliminates much of this distortion.

      Other recordings upsampled included recent ones, including the stunning Dorian Villa-Lobos String Quartets as performed by the Cuarteto Latinoamericana, the 5th volume of which has just been released. These quartets have amazing tonal colours and exotic rhythms, and may well be the best string quartet recordings ever made, certainly the best use of the Troy Savings Bank Hall I’ve heard.

      What did upsampling do here? Well, again it made the sound more vivid and realistic, revealing a greater and better developed ambient field, the result a more 3-dimensional soundfield. Another recording I found much more revealing and detailed was the Mobile Fidelity reissue of Simon & Garfunkel’s Bookends, where Roy Halee’s superb production and engineering could be even better appreciated. I’m still wandering around the house humming, “Wish I was an English muffin, about to make the most out of a toaster…” And I don’t even like Boysenberry jam!

      I could go on about numerous recordings, including our own, but I think I’ve pretty much made my point. As a final example, I heard things I’ve never heard before in our Loon’s Tunes from the Test & Reference CD, bits of bird and other nature sounds that had been veiled in normal CD reproduction.

      A further benefit of Purcell/Delius ownership is the superbly logical and methodical manuals, which are an excellent course in advanced digital audio. Once you’ve absorbed the descriptions of the capabilities of these superb components, you’ll also be very much up to speed on all things digital. Of course, as with any post-graduate course, the tuition fees are high, but worth it. Start saving, and then, start studying.

Andrew Marshall

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