Wednesday 28 August 2013

Analog vs Digital

We are now over 30 years on from the launch of the Compact Disc and the digital audio revolution.  And still the argument rages on - is Digital better than Analog, or vice-versa?  The proponents of Digital can offer a seemingly inexhaustable list of solid technological arguments in favour of the superiority of that format.  Meanwhile, the proponents of Analog seem to have very little to offer in support of their position other than to point out that, well, it just sounds better.  Why, after all these years, has the argument not yet been resolved?

As someone with a foot in each camp I continue to look for answers.  I totally buy the technological arguments, yet the best that Digital has to offer does not yet to my ears sound as good as the best of Analog (although Light Harmonic's Da Vinci DAC sounds quite a lot better than my own dated analog rig).  The more I work with digital audio - most particularly with high-resolution digital audio - the more convinced I become that Digital holds the key to advancing the audio state-of-the-art.  There is absolutely no doubt in my mind that the best Digital totally out-performs the best Analog in every single quantifiable respect, mostly by a clear margin.  And yet…

The best amplifier technologies out there remain Analog (although the rapid rate of progress in Class-D digital amplifiers bears watching closely).  State-of-the-art analog amplifier design generally holds fast to a handful of core principles.  First, we reduce the number of components in the signal path as dramatically as possible.  For example, we reduce the number of gain stages to a minimum, we try to reduce negative feedback as much as possible, and we go to great lengths to eliminate capacitors from the signal path.  Second, we prefer to use discrete components over ICs.  This is largely because we can optimize both the specifications for, and the implementation of, every individual component, whereas in an IC we cannot even isolate any specific circuit element, let alone measure or optimize it.  IC designers are not shy when it comes to circuit complexity, whereas the best Analog designers inevitably come up with the simplest circuits.  Third, we focus 90% of our design efforts on the Power Supply.

But once you get the signal into the digital domain, whatever you do to it, however you choose to process it, it becomes possible to measure and/or quantify exactly the effect of your process with absolute precision.  The equivalent of a circuit element is an algorithm.  No matter how complex or simple the algorithm itself may be, we can totally and absolutely quantify its impact.  And that impact may be zero.  Of course, some of these analyses may be extremely challenging to perform - almost anything involving a DSD bitstream comes to mind - but the principle remains the same.  Digital data is absolute and finite.  It contains no more and no less information than it is known to contain.  And we can measure and observe every last bit of it.

This is very different from Analog.  We can never know or even characterize the sum total of the information contained within an actual analog signal.  The output of an amplifier is ephemeral - it exists only for that one instant and is then gone forever.  If we want to characterize the output of the amplifier we have to be able to recreate it on demand.  Also, the very act of measuring an analog signal perturbs it.  This is not important if the perturbation is swamped by the various inaccuracies or uncertainties (or even the noise) involved in the measurement itself.  But the fact remains inescapable.  There are things contained within an analog waveform that we can never hope to measure.

So, given that there is so much apparently in favour of Digital, how can Analog possibly sound better?  I suspect that a part of the answer may be down to something I have touched on in previous posts.  When an analog audio signal is digitized, the most common ADC technology employed is the Sigma-Delta Modulator.  While the output of a SDM is digital data stream, it is not in the PCM format.  So it is then passed through a conversion algorithm to produce PCM.  I have argued that this algorithm may have sonic consequences.  However, today I wish to shine the spotlight elsewhere.  I want to look more closely at the SDM itself.

Inside the SDM, the input analog signal first enters an integrator, which is basically a big capacitor that gets gradually charged up by the input signal.  The output of the integrator is then digitized by a coarse quantizer - often only a 1-bit quantizer - driven at an extremely high sampling rate (usually several MHz).  The output of the quantizer is then fed back into the input of the SDM where it is mixed with the input signal before feeding the integrator.  The output of the quantizer is also the output of the SDM.  What I have described would make for an uselessly noisy SDM bitstream.  To fix this, the SDM is "noise-shaped".  This is done by placing a low-pass filter before the input to the integrator.  This low-pass filter must be a high-order design in order to produce acceptable audio performance.  It is important to note that all of this is done in the analog domain, and is typically implemented on-chip as a single IC.

So, what we have is a SDM-based ADC, where the analog signal is passed through a multi-stage (high order) filter and an integrating capacitor.  All done inside an IC.  These are all things that Analog designers have for decades sought to eliminate from their very best designs.  In short, when we digitize a high quality Analog signal, we do so by feeding it into a circuit whose topology has a serious potential for degrading the sound.

I wonder whether anybody has set about designing an all-discrete, audiophile-grade, SDM ADC?  There is really no reason I can think of why it could not be done.  However, although consumer customers exist for cost-no-object DACs - seemingly at ANY price the industry is able to come up with - I don't know if there is even a single pro audio studio anywhere in the world which would pay five figure prices for an equivalent quality ADC.  It would be a mighty interesting product, though…

I hate Rap

I really detest it.  It is missing one letter "C" plus the words "Total" and "Utter".

I hate hip-hop too.  Not only the sound - I won't call it music.  I hate the throbbing bass-heavy beat.   I hate the lyrics.  I hate the physical appearance of rappers/hip-hoppers, their fashion sense, their whole fuck-you culture.  I even hate their dance moves. 

Goddam - I'm turning into my parents!

So why am I listening to K'naan's album Troubadour?  And why, oh why, do I really like it?

Monday 26 August 2013

A first-hand lesson in Social Media

Leonardo Gonçalves is a popular Brazilian musician.  He has nearly 300,000 "likes" on his FaceBook page.  So what does that mean, compared to - at the time of writing - BitPerfect's 353 "likes"?  Well, two days ago he posted a short note on his FaceBook page, containing some kind words about BitPerfect.  The original is in Portuguese, but he has provided me with an English translation which I post below:

"I don't know how many of you 'seriously' listen to music on your computers;  I mean 'seriously' as in really paying attention to what you are listening to, trying to get a hold and the best possible source (WAV and maybe even high definition audio instead of mp3), also in terms of execution and what kind of monitors and/or earphones you use.

I also don't know how many of you use iTunes to organize your library and listen to music.

This tip goes to the maybe small group of people who fit both descriptions.  BitPerfect is a relatively cheap and user friendly program that instantaneously improves the audio quality of what you are listening to, once activated.

Do like their FaceBook page, do some research on the program.  I use and recommend it."

That's it.  Well, it seems that when Leonardo speaks, his fans listen.  Since that post, BitPerfect has had 54 new likes, of which 52 seem to be Brazilian.  It remains to be seen how many of those will follow up with a purchase of BitPerfect, but to BitPerfect's new Brazilian fan base I have this to say (courtesy of Google Translations!):  "Bem-vindo à família BitPerfect. Nosso objetivo na vida para fazer a reprodução de música de alta qualidade disponível para as massas com o menor custo possível. Se você ouvir música no equipamento que custa tanto como um Ferrari, ou tanto quanto uma bicicleta usada, acreditamos que BitPerfect não vai estar fora do lugar."

For those of you who might like to listen to Leonardo Gonçalves, here is a link to a YouTube collection of some of his videos.  The man has an excellent voice!

Thursday 22 August 2013

iTunes 11.0.5 approved

With apologies for the delay, I can now announce that we have been using iTunes 11.0.5 for a few days now with no new problems. Note that the skipping/looping problem I posted about on August 16th has not been addressed by this release, so at the moment we are working at developing a workaround for it that we can incorporate in a forthcoming update.

Saturday 17 August 2013

iTunes 11.0.5 released

iTunes 11.0.5 was released today.  This is not the same as the iTunes 11.1 beta that we have been testing for the last two weeks, so we have no experience yet with 11.0.5.  We will post here once we have approved it for use with BitPerfect.

Friday 16 August 2013

New iTunes Problem :(

A new problem within iTunes is beginning to emerge.  I don't know how widespread it is, and I cannot say for sure what it would take for users to observe it.  It does not affect all users by any means, but seems capable of suddenly appearing.  For example, none of our 30-odd member Beta Testers Team has reported seeing it, and only one system here at BitPerfect exhibits this behaviour, and did not do so as recently as one month ago.

For BitPerfect users, the symptoms are that snippets of tracks keep repeating in short 3-5 second loops, similar to the behaviour when iTunes 11.0.3 first came out and we had to release a BitPerfect update in response.  Whereas that previous problem had a known cause, and affected all tracks all the time, the current problem is more erratic, has been traced to an observable flaw in the behaviour of iTunes, though its root cause has not as yet been identified.  You can easily observe it yourself when BitPerfect is not even running, if you know where to look, and you have at least one track that systematically displays this behaviour.

When this looping/skipping starts, it can last for a few seconds or longer.  For instance, one user reports that it lasts for about one minute at the start of a track and then goes away, and comes back again a few tracks later.  Some users report that it affects AIFF tracks and not AAC tracks.  Others report that it affects 24/96 tracks and not 16/44.1 tracks.  Another user can make the problem go away by placing the affected tracks in a small playlist.  Yet another reports that files seem to start becoming "infected", and once affected will always play this way, and that the "infected" list grows slowly.  But don't fret - this is most assuredly not a Virus.

Here is what is happening.  Internally, iTunes is not updating its own track position slider.  So when BitPerfect asks iTunes for the position of the track position slider it gets back the wrong answer.  As we know, BitPerfect interprets this as meaning that the user has intentionally moved the track position slider, and so this will generally cause BitPerfect to re-start playback at the erroneous position, which is usually at a point 3 - 5 seconds earlier in playback, hence the loops.  This problem is not caused by the BitPerfect/iTunes communication itself, which can be proved by quitting BitPerfect and playing back the same tracks using plain iTunes.  If you keep a very close eye on the track position slider, you will see that it fails to correctly update itself from time to time.  Had BitPerfect been in charge of playback at those instants it would have created a loop/skip.

We have reported this to Apple, but we don't know whether or not they are responding.  Apple is a big black hole when it comes to this sort of thing.  What we do know is that the pre-release beta of iTunes 11.1 (which we are currently evaluating) exhibits the same behaviour, so a solution at the root appears nowhere in sight,

Here at BitPerfect we are trying to come up with an appropriate fix for this.  We think we know how to address it, and will release an update as soon as possible.