The DSD Player Choice Guide

Direct Stream Digital (DSD) is a digital audio format invented by Philips and Sony in 1999 and currently used on Super Audio CDs (SACD). Considered as nirvana in terms of musicality, the DSD was developed to correct defects in the CD-Audio standard, including the harshness of PCM signals, which are significantly under-sampled.

CD-Audio has been a lively and enduring success ever since it was launched in 1980, even more so than the best analogue storage media, the Philips audio cassette and the vinyl disc.

In 1980 Philips and Sony published the famous Redbook, what is considered the "Bible" which describes the operation of the Compact Disc Audio format and the sound digitisation technique using the Pulse Code Modulation (PCM) system.

The PCM is a digital representation of an analog signal, in which the height of the electrical signal is measured at regular intervals. This acquisition technique is called sampling and in the case of audio CDs, it takes place 44,100 times per second (for each channel). Each sample is encoded at 16 bits (binary characters), i.e. with a series of sixteen 0 or 1.

Philips and Sony had estimated that in 1980 44,100 samples per second were sufficient, mainly due to technical constraints. With this resolution, an Audio CD can hold 80 minutes of music. A doubling of sampling would have halved this capacity and decoders would have been offered that could process more data, but at exorbitant prices. In fact, the frequency of 44,100 samples/second poses a huge technical problem during decoding.

The weak points of the CD-Audio format - i.e. harshness, coldness, lack of naturalness - are due to the limit introduced by these 44,100 samples/sec, because in practice the frequency response allowed after decoding can only be half of the samples, i.e. 22,050 Hz (according to Nyquist/Shannon's Theorem).

In addition, irrelevant digital information is encoded in such a way that it does not have to be decoded, or at least in such a way as to mask it as much as possible. Immediately after 20,000 Hz, filters with very steep slopes are used. As a result, the essential harmonic frequencies are simply destroyed, to the detriment of musicality.

The DSD has 64 times the amount of samples in the CD-Audio

Aware of the problem, Philips and Sony revised their initial proposal in 1999, proposing the SACD and a new conversion method based on Delta Sigma technology rather than PCM. The first difference is that sampling is 64 times more frequent than on Audio CDs, with 2.8 million samples per second of the analogue electrical signal.

Second difference: each sample is encoded at 1 bit. As with CD-Audio, not all digitized data is useful and not all data considered irrelevant is "rejected" at the end of the bandwidth, but without the need for a steep filter to eliminate it during decoding. As a result, the harmonics are not destroyed and the music has an exceptional naturalness.

DSD vs PCM

A stereo DSD audio stream has excellent technical characteristics: a frequency response of up to 50 kHz and a signal-to-noise ratio of more than 120 dB.

Despite this technological superiority, the SACD did not get the success it deserved, because of the galloping dematerialization of music, distributed directly from the Internet in the form of ultra-compressed files (MP3, AAC).

The DSD format is not dead...far from it!

Ironically, in recent years it has even led to the rise of digital music in HD. Some time ago, the more experienced users found a way to extract DSD files from (protected) SACDs and then convert them to PCM format, in the form of 24-bit and 88.2 kHz FLAC files. The (not entirely legal) availability of free dsd music by downloading these files over the Internet has given rise to new consumption habits among music lovers, such as listening to these famous FLAC files from a computer with an external audio DAC (digitaltoanalog converter). The niche market for Audio DACs has evolved into a true Eldorado, at the same time as more experienced audiophiles have begun to take an interest - highly musical - in using external DAC converters with their computers.

How to listen to DSD files? Of course, with a DSD player! 

To decode a DSD file, you must have a DAC designed specifically for this purpose. However, 99% of the DACs built into Hi-Fi sound cards, external USB DACs, home theater amplifiers, or audiophile players are only capable of processing the signals... PCM.

Initially, very few electronic components were able to natively read the DSD and were then converted to PCM in real time. However, the quality remains outstanding.

There are native conversion chips with DSD support, including: ESS Sabre 9018, Wolfson WM8741, Wolfson WM8742, Texas Instrument Burr Brown DSD 1608, DSD 1702, DSD 1791 or DSD 1794, not to mention Asahi Kasei. It's only a matter of time before they are integrated into the electronics of manufacturers, home theater amplifiers and media players.

The very strong competition of the PCM DXD

Although perfectible in CD quality, HD version PCM encoding is widely used in the studio for burning albums. As technology advances, the sampling rate has increased to 192,000 samples per second, encoded at 24 or 32 bits. In 2007, the DXD PCM (for Digital eXtreme Definition) was introduced with a sampling rate of 352,800 samples/second (352.8 kHz), 8 times higher than the Compact Disc Audio, with 24 or 32-bit quantization. The PCM DXD format is currently used in music production (mastering) and very often... before conversion to DSD format. In fact, of the nearly 9,000 existing SACD albums, only 1,600 are digital DSD recordings. The others are derived from a PCM capture and were then converted to DSD.

Where to download DSD files (.dsf)

Where to get it? The sites that distribute DSD files are for example 2L and Native DSD. Qobuz or HDtracks sell studio-quality music albums, but encoded in PCM (FLAC, WAV or AIFF files) - however, in very high resolutions between 24-bit / 88.2 kHz and 24-bit / 192 kHz.

For the moment, the distribution of DSF files (DSD container) is reserved for some sites that offer legal downloads: 2L, Blue Coast Records, Channel Classics Records, Cybele Records or HighResAudio.

Warning: a DSF file takes up a lot of storage space: often more than 100 MB for 5 minutes of music. If you do not have a DAC or a player that is natively compatible with the DSD, you should use a Music Server (such as Cocktail Audio) that allows you to read it.

How to play files with a DSD player

The big dimensions and the transmission speed of the DSD streams make it impossible to transmit them via S/PDIF connections (optical, coaxial, AES/EBU). Only an HDMI, USB or i2s connection can stream a DSF file to a compatible DAC Converter. For greater flexibility, DLNA network protocol support should be extended to compatible units.

DSD64, DSD128 and DSD256

The DSD format as we know it today (DSD64 for sampling 64x audio CDs, or 2.8 MHz) will certainly only be a step towards an evolution of the standard that will be more widely adopted by studios and the general public. The DSD128 (5.6 MHz), already supported by the Cocktail Audio music servers and by many converters such as the CEC DA5. All that remains to be done is to change the habits of sound engineers to work in PCM.

In conclusion, if the DSD format is promising, there is still a long way to go before it completely replaces the PCM format and its successful containers such as FLAC or MP3.