Written by: Rob Pennock
The purpose of this article is to offer a brief guide to the constantly evolving world of high-resolution (hereafter high-def) sound. Lengthy descriptions of technical processes have been avoided, so if you want to know what a one bit-depth does to the dynamic range you will need to look elsewhere, but it has been necessary to give a brief outline of what numbers like 24/192 mean, file sizes. FLAC and the like.
If you have a degree in electronic engineering you may feel that X or Y should have been mentioned, but this is written by and for the sound enthusiast who wants some idea of what high-res can offer, not specialists. Nor have I addressed the vexed question of digital ‘remasterings’ (for want of a better term) of analogue tapes, which will be dealt with in a very much shorter piece in the near future
Back in 1982 in a flurry of publicity some quaint little shiny, plastic things called compact discs appeared on the market. These carried digital data in the form of 0s and 1s, which could be played through an analogue hi-fi system by purchasing a CD player which contained (as they still do) a digital-to-analogue convertor (DAC). Needless to say because the ‘majors’ had been making digital recordings for several years and they cost far less to produce than vinyl, they went all-out to promote them as an astonishing new medium which would transform the way we listen to music. So we could pump iron at the gym, or do the gardening, while listening to The Ride of the Valkyries or the Pastoral Symphony in sound of astonishing clarity and naturalness. If you fancied Jacqueline du Pré and John Barbirolli in the Elgar, or George Szell in Richard Strauss’s Don Juan, well, digital technology would bring these classic performances to breath-taking life by taking you closer to the master-tapes, uncovering unheard layers of detail, and you wouldn’t have to put-up with those horrible clicks and scratches it seems all LPs were bedevilled with. Certainly in the classical world this marketing worked remarkably well, and, within a decade or so, vinyl was dead. But there was a problem in that a lot of people and audiophile publications questioned just how good digital sound actually was.
What is arguably the world’s premier audiophile magazine, The Absolute Sound, would take a remastered Decca recording from, say 1963, and compare it with an early label LP, and in the vast majority of cases the original was far superior, while others would point out that new recordings were often full of digital glare, ‘ringing’ and edginess and sounded totally unnatural.
Then in 1993 a nuclear bomb exploded when the web became public domain and its rapid growth and availability meant that sceptics could talk to one another and make their views known to a far wider audience. At the same time there were those within the recording industry who recognised that the 16 bit depth/44.1kHz sampling rate (see below) CDs use was sonically compromised and sought something better, which in the first instance was SACD (the fate of the alternative DVD-Audio falls outside the remit of this article), which also suited the creators of CD technology, Sony/Philips, as it meant traditional Red Book1 CDs, or more properly Compact Disc Digital Audio, which they held the licence for, could continue, even if in a hybrid form.
PCM & DSD – Facts & Figures
Most Super Audio CDs have two layers, one of which holds what is called PCM data plus a very much larger DSD layer. What are PCM and DSD, which are formats used for high-res downloads?
PCM stands for pulse-code-modulation, which is a way of converting the analogue wave-forms instruments and singers – or in the case of remasterings, reel-to-reel tapes – produce into digital audio signals (the 0s and 1s mentioned above). This can be in a number of formats such as 16 bit/44.1kHz, 24/44.1, 48, 88.2, 96, 176.4 or 192 up to the highest generally available today, 24 or 32/352.8, which is DXD (Digital eXtreme Definition). What do these numbers mean?
Taking the latter first, at points on the analogue wave you have to take samples to draw a map of the curve, which in the case of 44.1kHz means 44,100 times per second. So this figure is the sampling rate. Each of these points has a bit-depth, which is usually 16 or 24. String these points together and you have a digital approximation to the original.
As those who burn CDRoms will know, in order for them to be read by a CD player they have to have a bit-rate of 1,411kbps, all this means is that you multiply the bit-depth (16) by the sampling rate (44.1) and because there are two channels, double it, which equals 1411.2. Commercial CDs are no different; they have to be 16/44.1.
Fairly obviously the larger the numbers the more information is collected. So all other things being equal – which as we will see, they are not – if a 79’59’’ CD holds (using Colin Crawley’s calculator2) 846.4 Mb of data, then a 24bit/192kHz file will hold 5.53 Gb, which is way beyond the carrying capacity of anything other than a DVD, and most CD players aren’t programmed to read these and/or 24/192.
Turning to DSD (Direct-Stream Digital), this auspicious sounding acronym derives from a process created in the 1970s by Philips, which it and Sony trademarked and used as a way of capturing the afore-mentioned analogue waves, which was then used as the format for SACD. The big difference between this and PCM is that DSD has a bit depth of 1, but a massively increased sampling rate, which in terms of an SACD is 2.8224 MHz or 64 times that of a CD; hence this is called DSD64, which is the lowest DSD rate (if you see DSF on a download, this means Direct-Stream File, which is how it is stored, with what is called metadata – for example, artist/track names or numbers, booklet etc.). Go to DSD128 and the sampling rate doubles, you then have 256 and very recently 512, which give some massive figures.
Finally, there is the simple question, what is Direct about DSD? Well here it becomes very technical, but in essence the pathway between the source and the loudspeakers in your home is far simpler than with PCM, so there is less processing going on, which lessens distortion.
What happened to SACD?
When these first appeared in around 1999 they were more expensive than standard CDs and some of the first discs were single-layer DSD, but either way you needed a special player to listen to the DSD layer, which would usually again be more expensive than a normal one. There was also a lot of discussion about just how good SACD sound was, with exaggerated claims made on both sides, which didn’t inspire confidence in consumers, and in the West they never really took-off, where it was left to smaller audiophile labels such as Bis to carry the flag.
Interestingly, South Korea and Japan never lost faith in them, so the ‘majors’ licensed smaller companies such as Esoteric to produce high quality remasterings from their back-catalogues and in some cases produced in-house discs which were not marketed in the West. Then as interest in high-def sound grew they started and continue to make a worldwide comeback as both major and independent labels promoted them again and it is worth bearing in mind that unlike PCM the DSD layer can hold multi-channel tracks.
High-Definition Downloads & FLAC
As the web grew and connection speeds increased, several enterprising companies started to promote that they recorded in high-def and you could download the same quality files from their, or a third-party, websites. In most cases these were PCM, but some also offered DSD. To begin with 24/96 and DSD64 were the most popular formats, but as time went by 24/192 appeared as did DSD128, then there was DXD and DSD256 and in the last few months DSD512.
Having discussed PCM file sizes just how big are DSD downloads?
Well, the Richard Strauss Tone Poems with Manfred Honeck and the Pittsburgh Philharmonic Orchestra on a Reference Recordings DSD64, which has a running time of 59.24 isn’t huge at 2.34GB. Turn to Strauss Tone Poems Volume 2 with Vasily Petrenko and the Oslo PO from a LAWO DSD512 download and the 76.25 programme is a whopping 24.1GB. Schubert’s Winterreise with Thomas Oliemans and Paulo Giacometti from a Channel Classics DSD512 download lasting 71.24 has a file size in direct proportion to the length of the Petrenko at 22.5GB, despite the Oslo PO producing far more volume and complex sounds. If the Honeck was DSD512, the file size would be 8 times larger and it’s as simple as that. (For DSD512 and in many cases DXD you have to go to NativeDSD.com3 to download the files).
If we then look at the Petrenko in 24/192, you have a download size of 2.49GB, however if you put the figures into the Crawley calculator the actual size is 4.9 or 5.3GB depending on whether (and here your eyes may begin to glaze over) you measure the size of the kilobytes per second bit-rate using the binary figure of 1kB = 1,024 bytes, or the decimal, which assumes 1kB = 1000 bytes.
The reason for the difference is FLAC (Free Lossless Audio Codec) which retains the bit and sampling rates of the original but lessens the file size by various degrees depending on which level you choose, without – unlike lossy formats such as MP3 – hacking chunks out of it to save space; virtually every recording and remastering company uses FLAC for its PCM downloads. The alternative is uncompressed WAV (Waveform Audio File Format), which is what you use if you want to burn a playable copy of a CD. Having listened to numerous FLAC files and their WAV equivalent – including the Rattle, BPO, Sibelius Symphony cycle – the latter does provide slightly better sound, but it seems unlikely that anyone is going to be supplying large quantities of high-res WAV files anytime soon.
Software and Hardware
Unfortunately, you do need specialist software to play high-res files, as neither Windows Media Player or iPlayer can decipher them, so you have to download alternative applications, of which there are only two, JRiver Media Center and HQPlayer Center (see below), that read everything up to DXD and DSD512 without compressing or converting the original, including multi-channel DSD, and, while we aren’t looking at it here, the app must be able to handle streaming, which can offer high-res PCM formats. With DSD in order to get the best possible sound you need to play the files in what is called native mode, which means there is no filtering between the application and your amplifier.
Looking at the two mentioned above, the JRiver Media Center does an excellent job and isn’t too expensive. In terms of sound – and these apps do sound different – the Rolls Royce is HQPlayer, which is a techie paradise, boasting multiple filters, spatial settings for surround sound, excellent on-the-fly conversion from PCM to DSD and vice-versa, etc., but this handles very few formats and is expensive. Nevertheless, I use this along with a freebie called Foobar, which, via add-on components, reads just about every audio format known to humankind, but not rather strangely DSD512. Both HQPlayer and JRiver offer a free-trial, so you can decide what suits you best.
Turning to the hardware, you get stand-alone DACs and those which come as part of an SACD or CD player with a USB input, which connect to your amplifier. It would be nice to say that these all play everything, but this is far from the case, and as with the app it must play DSD512 and DXD as downloaded without alteration and DSD in native mode. You can also use the DAC to listen to Radio 3, YouTube and the like. All require downloadable drivers. The same provisos apply to interfaces where the software is installed onto a separate unit which you load with the files you want to play, it imports the computer operating system it is connected to and then feeds the DAC, thereby eliminating the computer’s less than optimal sound circuitry.
As ever with hi-fi equipment you need to try different ones out and not be afraid to challenge dealers who might say “oh yes, this plays DSD256”, which doesn’t mean what goes to the amp is 256. If you buy online, study the spec which should say which formats are supported and contact the manufacturer if you are unsure about anything. As a guide, you are going to have to spend a minimum of around £550 to get a great-sounding DAC that does everything listed above.
As mentioned, from day one not everyone was satisfied with CD sound, and despite improvements in technology with the growth in LP sales yet more listeners realised that silver-discs were not the universal panacea they had been promised. Others began to listen far more critically and felt able to voice their concerns online, while one of the world’s most highly respected recording engineers told me (so long as I didn’t mention his name!) that CDs were the digital equivalent of a music-cassette, and that the high-def-download pioneers knew that these sounded better. And when companies such as Hyperion and Channel Classics started offering the downloads in 2009/10, CDs were, by digital standards, old-hat and downloading – and now streaming – was a possible future.
There are innumerable online articles, blogs and the like where contributors use techno-speak to try and justify their views on CD and high-res sound, whereas all that actually matters is what you hear, so below are a few comparisons.
Back in 2012 Hyperion recorded Florian Boesch and Roger Vignoles in a magnificent recital of Schubert songs called Der Wanderer, which it released in 24/88.2 and of course on CD. I originally reviewed the download, but having now listened to the CD, the former has a better dynamic range (although it is not state-of-the-art), the performers have more body and presence and you get a better idea of the All Saints’ Church, East Finchley, London acoustic, where the reverberation time is well-controlled.
Turn to Gabrieli for Brass, Venetian Extravaganza from Linn in 24/192 and the dynamic range is superior to the CD, which should be the case given that high-res spans 144dB, CD 96dB. More importantly Linn also chose a church, St Jude-on-the-Hill in Hampstead Gardens, London. Here the reverberation time is only about 3.5 seconds, which Linn told me was achieved by situating the players under the tower and the careful placement of just two microphones. However with high-def you are aware there is still a large space around the performers, the instruments sound more life-like and the image has greater projection than the CD or 24/88.2.
Then we have Rachel Podger and Brecon Baroque in Vivaldi’s Four Season in DXD from Channel Classics where the bass-line in the opening movement has tremendous bite, you can hear the bows hit the strings in a way that no CD can hope to equal and there is even greater weight and power than on the 24/192 version. But this is also available in DSD256 and 512, the first of which (played in native mode) is cut at a slightly lower level, the overall balance is more recessed, the acoustic even more tangible and the instruments have a softer edge; in effect this is more analogue-like. If like me you love vinyl, then I suspect the DSD will appeal more, but it is entirely down to personal taste.
This brings us to DSD, and I am not going to compare the three recordings below with CD because it is pointless, they are better for all the reasons above and sound less digital, but if we look at the aforementioned Honeck in the Strauss tone poems in DSD64 and compare it with their recent magisterial account of Bruckner Nine in DSD512 from the same label several things become apparent. First, while DSD64 captures the acoustic of the Heinz Hall for the Performing Arts and there is a fine sense of depth, with 512 you can almost walk into the hall and orchestra. Second, while all of the sections of the orchestra have fine presence and body and instrumental timbres are vibrant in 64, at the higher rate the brass rasp even more, the timpani crash out, in an area where digital has never been able to equal the finest analogue, the woodwind are far more life-like (the oboes are clearly reed instruments), the strings have an analogue like lustre and the whole image has a real wow factor. Finally we turn back to Oliemans and Giacometti in Winterreise, which we can compare with the Boesch, Vignoles recital, except there isn’t any comparison, the DSD512 again having a walk-in sense of space, the distance between the artists is tangible, Oliemans is more human, indeed his timbre almost matches what you find on golden-age vinyl and the piano actually sounds like a piano not a hologram. On its own terms the Hyperion is excellent, but the DSD is as good as digital sound gets.
Hopefully the above provides an insight to high-res downloading. Certainly as someone who has always found CD sound at best problematic, it comes as balm to the ears and DSD512 stands at the pinnacle of modern digital sound, which everyone should hear. If you have any questions please leave a comment and I will endeavor to respond.
- First published in 1990 by Sony/Philips the Red Book contains the technical specifications for CDs, the other colours are Scarlet (SACD) Yellow (CD-ROM), Orange (Recordable CD), Green (CD-interactive), White (Video-CD), Blue Book (Enhanced CD), the Rainbow Book covers defunct MiniDiscs. Unsurprisingly it and the information it contains are not free
- Colin Crawley’s audio file size calculator
- NativeDSD offers a very large range of high-res classical titles in a number of formats, most of which are not available from the original labels. You get a similar – if very much smaller – thing with Hyperion, where if you want a Signum Classics high-def download you go to their website.