Tag Archives: pulse density modulation

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolinas Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Threatening

There’s an intriguing dynamic in people; feeling threatened by other beliefs.

We just launched the NuWave DSD, a great and economical entry level DAC. No sooner was it released when we get a note from a well known engineer proclaiming DSD a sham, a Sony storage mechanism pulling the wool over unsuspecting eyes. We are told by this engineer that before too long the blindfold will be removed and we’ll finally understand what a scam DSD is!!!

And, of course, we’re among the evil people perpetrating the ruse.

First, of course, the person is completely misguided and incorrect. DSD is a format (not a storage medium) that uses pulse density modulation where PCM is another format that uses pulse code modulation. They both have their benefits and problems; neither is perfect. I like and listen to both, though my preference leans towards DSD as closer to analog than PCM. But I do not get angry over the situation and question why anyone would take this personally.

Similarly I do not understand why people are threatened with tattoos, or piercings. Are they something I would ever consider? No, but I don’t feel threatened by them. That segment of the population feels compelled to stand out against the norm. When I was a lad some of us grew our hair long, smoked pot and listened to rock and roll, much to the horror of our parents. I don’t typically feel threatened by other beliefs or viewpoints when they do not affect me. But getting worked up over PCM or DSD? Really?

I understand feeling threatened when our homes, children, livelihoods, or safety are at stake. But personal beliefs and practices that do not affect others? I guess I just don’t get it. Maybe I am being shallow or don’t want to look.

Thoughts?

Wait for it

Converting analog to DSD is a pretty simple process in some respects.  Even simpler than PCM.  But here’s a case where the concept may be simple but the execution is not.  However, in order to understand how it works, we don’t really need to wade into the details.

Basically we have a fixed clock running at 2.6MHz (single DSD, analogous to 176.4kHz in PCM) or twice that at 5.2MHz (double DSD, analogous to 352.8kHz in PCM).  This clock is just plugging along making its little square waves that will eventually become the actual bits that form the music.  In fact, the 1-bit we talk about is from this clock, producing a steady stream of 1-bits all at the same speed and interval.

So, picture a a guy standing at a gate.  Behind this gate is the steady stream of bits moving along at 2 million, 600 thousand times a second.  The gatekeeper’s job is to open the gate and let some of the bits through the gate whenever he hears some music.  If he hears no music, the gate is shut, none of the little bits can escape.  If he hears some music faintly playing in the background, he very carefully opens the gate and lets a few of the bits out.  The louder the music he hears, the more bits he lets out.

Now, add to this picture a neighbor to the gatekeeper that’s in on this scheme to release bits.  The neighbor can hear the music with one ear and with the other ear, he’s able to sense the number of bits being released by the gatekeeper.  His job is to compare the number of bits released with the loudness of the music and if there’s not enough, or if there’s too many, he signals the gatekeeper to release more or lessen the flow.

Between the gatekeeper releasing bits and his neighbor, keeping a watchful eye on his activities, the number of bits goes up and down in direct proportion to the music (the neighbor providing a constant feedback to keep the system correct).  That’s DSD or Pulse Density Modulation.  Now, remember a couple of things: the bits are always the same size, always the same speed.  All we’re doing is letting more (higher density) or less (lower density) through the gate.  If you just open the gate and let all the bits flow without any change, that’s as loud as the music can ever get.  Close the gate and let nothing through, that’s as quiet as it can get.

Keeping that picture of changing density in your mind and remembering that the bits are actually just energy – electrical energy – then it isn’t too big a leap to imagine that moving electrical energy can make music.  After all, isn’t analog just moving electrical energy?  Sure it is.  In fact, the only difference between the DSD moving energy and the analog moving energy is all those little stops and starts of the single bits.  How do you remove those and fill in the small gap between bits?

A DSD DAC which, in its simplest form, is nothing more than a resistor and a capacitor.  Remember?  Ten cents worth of parts go into a simple DSD DAC and those parts smooth out all the transistions and you are left with …… wait for it …….

Analog.


Paul McGowan – PS Audio, Intl.