Sunday, 17 November 2013


BitPerfect Sound Inc. has been interested in DSD playback since early 2012.  Initially, our interest was in learning about the format, and understanding how it works and how the various playback solutions functioned.  We wanted to understand how Sigma-Delta Modulators work (these are the complex devices which create a DSD data stream), and to understand why - also how, and even if - DSD sounded different to high-resolution PCM.  We acquired some software, co-opted some fellow-travellers, and began to experiment with converting PCM to DSD and vice-versa.

One of the first things we discovered was that different software which performed the DSD-to-PCM conversions produced PCM tracks which sounded markedly different.  On one hand, this should not have been a surprise, since we knew that the conversion process is inherently not lossless, but on the other hand you can never be certain whether the differences will actually be audible, given the superb audio specifications claimed for both DSD and high-resolution PCM.  It was therefore a considerable surprise to us that the differences were not only audible, but that the magnitude of the differences was so great.  This was concerning to us, since even the poorest performing (at least based on our subjective assessment) software is being used to produce commercial products for purchase and download.

We were interested to see if we could understand the factors which can result in adverse sonic characteristics.  It turned out that, yes, we could identify those factors, and having done so we used those results to define an algorithm and methodology which we believed could produce significantly improved results.  After substantial testing we came to the conclusion that our results are audibly superior to all of the the alternatives currently on the market.  We have now reached the point where we know of no way in which to significantly improve upon these results.  These advances are now available to you as DSD Master.

[Note:  It is interesting that the opposite is not the case.  Converting PCM to DSD is a technical challenge which is exponentially more complicated both to understand and to execute.  We have a lot more work ahead of us before we can hope to launch a PCM-to-DSD converter for which we can make similar claims.]

So what kind of technologies lie behind DSD Master?  DSD-to-PCM conversion is at its core a two-step process.  First, the DSD datastream is passed through a low-pass filter.  Second, the output of the filter is passed through a sample rate converter.  Optimizing these processes is, at least in part, a matter of trading off several factors: (i) the time taken to perform the calculations; (ii) the amount of memory needed to store the intermediate calculation results; and (iii) the minimum CPU specification demanded; against the performance of the filter and converter.  The design of filter is crucial here as the filter's characteristics will impact - among other things - the frequency and phase responses of the converter (and also the impulse response, which is a convolution of the frequency and phase responses).  Each of these characteristics is very important, and you cannot achieve ideal behavior from all three simultaneously.  A critical aspect of filter design comes from your choice of which compromises are acceptable and which are not.  Additionally, if you expect a lot from your filter, you must be aware of the numerical precision with which both the hardware and software will execute the calculations, and assure yourself that it will be able to deliver the accuracy you require at the output.  Finally, you can easily throw away all the benefits of a well-executed filter by adopting a sample rate converter of less than comparable quality.  Where compromise is called for, DSD Master has chosen wherever possible to sacrifice process speed for performance.

As we developed this product, we were thinking that a significant motivation for BitPerfect users was to enable them to make the best possible versions of their DSD tracks so they could load them into iTunes and play them through BitPerfect.  But this was not too persuasive an argument, since if customers had gone to the trouble and expense of purchasing DSD music, then they wanted to play it natively, and would probably instead use a different player to play them.  This was a doubly frustrating realization for us, since BitPerfect internally has long been able to play DSD.  The problem has always been that you cannot load DSD files into iTunes.  We realized, however, that we could use DSD Master as the basis for a very elegant solution to this problem - we call this solution our "Hybrid-DSD" file.  You can read more about that here.  These "Hybrid-DSD" files can be loaded into iTunes, will automatically play PCM music if iTunes is used without BitPerfect, and, if BitPerfect is in use, will play DSD if the DAC supports it and PCM otherwise.  This, finally, is the solution we have been looking for for some time.