I used to own Quad electrostatic loudspeakers – the original ESL 57’s. Although they had some significant shortcomings, they were, in their day, the most transparent set of speakers on the market. Quad’s motto was, and still is, “the closest approach to the original sound.”
Ironically, today, that honor may still go to quad. Not the loudspeakers, but a recording technique called Quad DSD. What is it? It has to do with the way Super Audio Compact Disks SACD‘s were engineered. They used PDM (Pulse Density Modulation) which is now called Direct Stream Digital (DSD). PCM (Pulse Code Modulation) is used in regular CD’s. DSD produced a superior sound which relied on the ultra-fast sampling of a digital signal using one bit at a time rather that 16 bits in PCM.
But as we know, SACD failed to reach a significant level of acceptance by the buying public. What went wrong? The discs were more expensive, they had built-in copy protection , and they required special playback equipment which was more expensive. There was no backward compatibility and they were poorly marketed. In addition, as music downloads were taking off, and SACD was becoming obsolete. Moreover, the promising recording technology of DSD was not executed to its fullest potential.
Today DSD files which can be downloaded. These files are called DSD 64 files because they have a sampling rate that is 64 times faster than a CD. This rate is 2,800,000 times per second (2.8MHz), which was the original sampling rate of SACD when it was first introduced. This high sampling rare was thought to be so fast that it fool the ear into thinking it was listening to a analogue signal.
But the DSD recording process has moved on. Now files are available at twice that sampling rate of the original DSD. Why the higher rate? Well, some recording engineers still prefer the sound of PCM over DSD. DSD is only 1 bit, whereas CDs are 16 bit, DSD is actually noisier in the highest frequencies that PCM. This noise must be filtered out, but some people still here what is left over. This issue seems to go away if the sample rate is doubled to 5.6MHz. This higher rate is called DSD 128. The noise is moved up to a higher frequency that is undetectable for most listeners.
What if we double the sampling rate again? Apparently this opens up a whole new world of sound, at least as some engineers hear it. We are talking about Quad DSD or DSD 256 at a sampling rate of 11.2MHz. When a recording is mastered this way some professionals are saying they are getting the same sound that they are hearing in the studio or at the performance hall in the case of a live recording.
To get this type of performance, however, we need to stay with the DSD process from start to finish. Intermediate steps in the production may degrade the sound. (In many cases, DSD is transferred to PCM along the way because it is an easier format in which to mix and master.) The staring point in the recording process is also very crucial. If we are remastering previously recorded material, the quality of source material is paramount. For example, are we using master analogue tapes? They usually sound better than many of the earlier digital tape recordings. This may be one of the reason that vinyl can sound better than digital. (Another reason may be the way in which music was originally recorded in the analogue days. Fewer mics and less mixing captured more of the hall sound.)
Of course, analogue tapes have their own drawbacks. They deteriorate over time. They are noisy and must be filtered in the highest frequencies. This is why direct to disc vinyl recordings are potentially better sounding than those started with analogue tape. (I remember that in olden times a live Friday night broadcast from the Library of Congress heard over my Marantz 10B tuner was the closest approach to the original sound for me.)
But what may be of greater interest is the comparison of brand new Quad DSD recordings from start to finish to those started with master analogue tapes. Some engineers have said that these type of recordings surpass all others, including the ones using master analogue tapes. Could this be the future of quality recordings of Classical and Jazz music? Could this be the closest approach to the original sound?
Where does Quad DSD leave PCM and normal DSD downloads, and where does it leave MQA? Well the Quad DSD file size is about 8GB, compared to a conventional DSD file of about 3GB and a double DSD of about 5GB. The size of the Quad DSD download file may be prohibited in many cases, especially in streaming audio and portable use. A MQA file is just 40MB. (For comparison a conventional CD has a file size of 600 MB., a 24-bit/96kHz FLAC file is 73 MB, and a 24-bit/192kHz version is 142 MB,) Here is a visual comparison:
Now it is time to let you in on a little secret. I may not be new to you but it has been to me. The quality of the mastering is still of overriding importance. There is more to a good album than just the final sampling rate. The key is to find something that is 1) Directly recorded to DSD, 2) Edited in DSD as opposed to PCM, 3) and output as DSD. Higher than standard DSD is preferable, but if these 3 requirements are not satisfied, then Quad DSD files are probably not going to sound any better that standard DVD files, if as well.
Case in point, mastered for iTunes files can sound exceptionally good even though they are ultimately presented in 256 kHz AAC. If they started out with higher quality formats we can still hear some of the advantages of that sound. Almost everything is recorded in a high resolution digital format today. Files submitted to Apple to be used in the “Mastered for iTunes” format must be of this higher resolution. Try Prime Cuts (The Columbia Years 1987-1999) Grover Washington Jr. as an example of how good AAC can sound, especially when processed by Audirvana Plus.
If you want to listen to Quad DSD you must have a compatible DAC. The wonderful Dragonfly Red is great for MQA and Flac files, but will not handle Quad DSD. You will need a more powerful DAC which handles higher sampling rates.
The CHORD Electronics Mojo ($529) will get you into Quad DSD at a fairly high sound quality level. The device is lightweight with a built-in chargeable battery. It was designed for portable use but it works well with a desktop system and is of sufficient quality to be used with any home audio system. It will play almost any audio file that you can find, up to 768kHz 32bit. Unfortunately, the Mojo is not compatible with MQA.
A lower price $200 alternative would be the Optoma NuForce uDAC5 USB DAC. Although this is a tiny DAC, as you can see, it will play very nicely with your computer and Quad DSD files.
Where to find Quad DSD releases? Go to Native DSD Music. The catalogue is not large, but it is just getting off the ground. You are probably going to see mostly Jazz and Classical music. No offense, but this quality of sound and price point is not going to be supported by many popular music enthusiasts alone. For many, MQA files or streaming should serve just fine. Nevertheless there will always be those who are looking for “the closest approach to the original sound.”