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.