Tag Archives: PCM

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

Too many “weeds” here from Paul, but interesting to some.

Sample rates

There sure is a lot of confusion over sample rates. We hear about CD-quality sample rates at 44.1kHz (and its multiples), or another common sample rate, 48kHz (and its multiples), and then there are multiple higher sample rates (176kHz, 192kHz as examples) and of course DSD.

Lots of numbers. All very confusing.

Perhaps a short primer would help.

First, what is a sample rate? Simply put, it’s a snapshot of the audio signal. A slice of time where we capture the voltage level of the music signal. The number of times per second we take that snapshot determines the sample rate. (Bit depth determines the loudness range we can capture within each sample)

First, what’s the difference between 44.1kHz and 48kHz and why do the two exist? The former is what Sony/Philips set as a standard for the Compact disc. When we do higher sample rate versions of this standard we get 88.2kHz, 176kHz and so forth. The latter, 48kHz, is the standard the “pros” use (because, well, they can’t use something as conventional as consumers, now can they?). 48kHz gives us multiples we’re familiar with like 96kHz, and 192kHz.

What’s painful about the above two standards is the difficulty moving between them. When recording studios record at “pro” sample rates of 48kHz they then have to interpolate down a few Hz to 44.1kHz to make something we poor consumers can listen to.

Silliness.

When we nerds talk about sample rates we use different terminology. We base our discussion on how many multiples of the base frequency (44.1kHz) are in play. So, for instance, the CD sample rate is referred to as 1fs. Its multiples are 2fs, 3fs, etc.

The sampling frequency or sampling rate, fs, is the average number of samples obtained in one second (samples per second). Think of 1fs as the minimum baseline to capture 20Hz to 20kHz.

While we might be familiar with all the differing PCM sample rates, DSD brings in a whole other dimension with its far higher sample rates. For example, standard DSD is 64fs while double rate DSD is twice that at 128fs. So what’s that mean? Well, 1fs is running at 44,000 times per second, while 64fs is running at 64 times that frequency, or 2,822,400 times per second! That’s fast, man.

And, while DSD is so much higher of a sample rate as to raise a few eyebrows, it’s instructive to remember it’s a 1-bit system compared to a basic 16-bit system like PCM (remember that the number of bits is needed to measure amplitude). This boils down to something less hair raising if we do a bit of math. 64fs (1xDSD) runs at a very high clock rate of 2,822,400 Hz (2.8mHz). Now, simply divide that by 16 (the number of bits in a PCM word) and guess what you get? A sample rate of 176kHz. Sound familiar? 176kHz is the same as 4fs PCM. So, while PCM requires 16 bits to adequately measure amplitude, and DSD needs 16 single bits to do the same, it all kind of works out in the end. (Don’t take what I just wrote about DSD and 16 bits as literal. I use it only as a means of helping form a picture. DSD is far more complicated, using a Sigma-Delta Modulator, noise shaping, etc.)

Without getting too much more in the weeds, that’ll give you a brief simplistic overview of sampling rates.

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

I’ve got great DSD recordings, as well as great PCM recordings. Which format doesn’t tell the story on how good a recording sounds. Lots of other reasons why things sound the way they do.

Is higher better?

Working with DSD and PCM has been a real learning experience. The two formats sound different from each other though it is unclear why. Is it the analog to digital conversion processor? The DACs? That DSD is closer to analog? They are all different technologies.

On the one hand, DSD runs at a much higher sample rate than any PCM. Single rate DSD is 64 times higher sample rate than CD quality PCM. Yet, there’s not much more audio bandwidth available because of that higher sample rate.

And then there’s PCM. Few today would argue that 44.1kHz is the bare minimum required for decent reproduction. Anything less and we lose the audible frequency range. But double that, and now we can capture twice what we are capable of hearing. And 4 times that (176kHz) and we’re able to capture 80kHz. Much more than we can hear and more than sufficient for phase linearity.

Yet more seems better: 2X, 4X, 64X, 128X, and so on.

We don’t know if the “better” we are hearing is due to the change in architecture or sample rate or both.

But, in a way, what does it matter?

I have heard CDs trounce 192kHz versions just as I have heard DSD smash anything PCM.

In the end, I don’t think higher is necessarily better any more than I think lower is always better when it comes to distortion.

Gotta listen.

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

Blind squirrels

There’s an old saying that even a blind squirrel on occasion finds a nut. A humorous aphorism about stumbling into success.

The more we get involved in the recording industry the more convinced I become that the paucity of great recordings comes from the same set of circumstances dictating the quality of the average home stereo. Most people wouldn’t know what we audiophiles consider truly great sound if their lives depended on it. Run-of-the-mill recording engineers included. The majority of their work is by audiophile standards mediocre. Once in a while, they stumble upon a great recording.

At Octave Records, we record exclusively in DSD because it sounds better than PCM and analog tape. But it’s a pain in the butt to edit which is why few engineers take the time and effort to use it. And, if what you’re working with sounds great to you, why would you bother?

Audiophiles know what remarkable sound is.

We’re a rare breed of sighted squirrels.

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

Most of what we listen to is PCM and with a great DAC, like the T+A DACS’s, PCM can sound fantastic.

Vinyl best

In my earlier post, Audio Pedigree I waxed on about how nice it would be to know the true origins of our music’s recordings. Remastered vinyl “improved” by digital enhancement from the original analog tape is rarely as good as the original and often worse.

This prompted a few juicy questions about our own Octave Records process as we move into vinyl. While we’re completely transparent as to the recording methods and source materials, it would seem to some that vinyl mastered from DSD falls into a similar category as the aforementioned digital remasters I do not like.

Not so.

The ultimate quality of vinyl is achieved by what we used to call Direct-to-Disc recording. Where the long-ago norm was to first record on magnetic tape then transfer to vinyl, a few labels skipped the tape recorder altogether. Artists would play live while vinyl cutting engineers went direct to the lathe. These direct-to-disc recordings were amazing but not because of any superior cutting techniques.

What made direct-to-disc recordings sound so great was the elimination of the magnetic tape recorder. That was it. Tape recorders have limited dynamic range—less than what’s possible on a vinyl disc.

So the problem is in the recorder, which is why it seemed to make sense to record digitally. Digital recorders have dynamic range capabilities that far exceed the limitations of vinyl. Thus, with digital, it should be possible to obtain the same performance as we got with direct-to-disc. And while that is true when it comes to dynamics, it isn’t true when it comes to sounding like the live event.

This is where we draw the line between PCM and DSD. PCM can often sound artificial while DSD in the right hands sounds analog-live.

A new era is upon us. It is now possible to create direct-to-disc quality vinyl without requiring the musicians to play live.

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

Audio pedigree

Pedigrees authenticate bloodline lineage. They’re important for dogs, royals, and source materials.

If you’re hoping to purchase an analog recording, it’s not genuine if it was first recorded digitally. Which is why there’s often so much confusion around modern LPs or even remasters. I shake my head when I learn a particular vinyl LP released remaster was first digitally transferred from analog tape.

That’s a mutt.

In a similar vein, it’s unhelpful when labels offer us versions of their libraries in multiple formats without being clear as to their pedigree. First recorded in PCM then released in both DSD and analog does not a DSD or analog recording make.

Here’s a vote for transparency into proper breeding.

If I want to purchase only purebred DSD recordings, I want an accurate pedigree.

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

I don’t necessarily agree with this, but PS Audio is heavily invested in DSD, with their top of the line DAC, converting all PCM recordings to DSD. At its best and that means the recording and playback abilities of our stereo systems being able to pay back DSD, DSD does sound better than PCM.

However, almost all of what I have, and by a lot, is PCM and it sounds fantastic, as long as the recording allows.

Sweeping statements

Here’s a subject I am perhaps more guilty of than most. The practice of making a sweeping statement about how everything is one way or the other. This is wrong and this is right. This matters and that does not. This guy’s a liar, and this one always tells the truth.

The problem with this line of communication is two-fold: nothing is always one way or the other and we cannot know everything.

I find myself making sweeping statements in an effort to emphasize a point important to me. DSD always sounds better than PCM. And you know what? In the examples I have experienced, that happens to be true. Unequivocally true. Thus it must be universally true—only, it isn’t.

This is how divides happen. When all you have ever experienced suggests one conclusion, then it must be the same for everyone else—which is true only in the case where others have experienced exactly what you have.

If our goal is to effectively communicate then perhaps it’s best to include the caveat “in my experience”. That’s a hard one to get wrong.

I’ll do my best to be better at that.

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Inc.

The live myth

Just a reminder that if you’re attending Chicago’s Axpona, come by and say hi tomorrow, at 4PM. I’ll be one of the cranky old guys up on stage in the Legends Forum.

There are no perfect recording or playback mediums. The much sought after goal of reproducing live music from recordings in your home is mostly a myth, though we often catch glimpses – snippets of the thrill of what it might sound like – sometimes outright fooling us into turning our heads because it sounds like someone is playing in the room. But consistently fooled? Not in my experience.

And yet claims of one playback medium excelling over another swirl like Minnesota black flies in June.

I promised in yesterday’s post on mastering limitations that I’d mention some areas where digital doesn’t hold a candle to vinyl in a technical sense. Perhaps the most obvious is the fact vinyl’s analog. And analog is the gold standard. Analog is continuous, infinite in resolution, and defines the medium conveying recorded music: the output of a microphone. Digital’s performance is always referenced to analog’s gold standard.  Sony’s original marketing claim of Perfect Sound Forever suggested digital is a carbon copy of analog (which, of course, isn’t true).

Digital’s proclamation of perfection is kind of like the artificial sweetener industry’s claim that their product is “indistinguishable” from their gold standard – sugar – a claim we can argue about all day long – but the point is the same. Both are attempting to be as good as the reference. Never better. And if someone’s claiming “better“, run like hell.

I don’t want to focus too much on the good and bad of digital, though most of you know my stance on it. DSD is closer to analog than PCM – and not by just a little. Sure, there are pundits that hear more detail and resolution from PCM than DSD, even if the PCM is a copy of the a DSD recording. That’s a subject we’ll likely jump into when we take a breath. But for the purpose of this discussion between the two major format groups – vinyl vs. digital – I will simply reiterate that both from a technical standpoint and from my own listening experience, DSD is closer to analog than PCM of any resolution.

But regardless of your opinion on the matter, here’s the thing. Both vinyl, DSD, and PCM’s goals are the same. The accurate reproduction of the original analog waveform in all respects.

Vinyl attempts to capture the analog using analog means – while PCM strives to do the same thing with numbers, DSD with varying degrees of energy density. In each case, the goal is the same.

And none get it right.

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?

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

Taking out the garbage

I mentioned in yesterday’s post it’s not a good idea to rely upon a low pass filter to reduce transient input problems if it is in the feedback loop of an output stage. The raw output of a DAC chip has lots of high frequency components that can agitate an output stage into sounding aggressive, bright, and unpleasant. The unfortunate proof of this can be found in DACs of all prices.
Modern DAC chips have more high frequency garbage than those of old because of higher sample rates for PCM, and greater noise levels with DSD. The stress on output stages following the DAC chips are at an all time high.

One simple method of reducing the stress on output stages is the use of a simple, passive filter between the DAC and the output stage. The chain would look like this: DAC raw output->passive low pass filter->output stage. Passive filters do not get upset by what you feed into them. Their output is simply a function of their configuration.

Why is this method preferable to redesigning the output amplifier to be less affected by its input? Because pre-cleaning noise allows the output amplifier to be designed with best sound first, immunity to noise second. The end result is a much better sounding output stage, free of transient overload.

Both methods work and measure well. It is the sonic differences that matter and those engineers that listen to their designs will nearly always triumph over the technologists who just measure.

Asheville, North Carolina ‘s Home Theater and Audio specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

It sure ain’t all the same

Yesterday we sharpened our understanding of why the multitude of digital storage mechanisms sound different despite the fact they produce the same data. What we learned is that while the data may be identical, its timing, noise levels, and quality presented to our DAC is not. In the same way we likely would not question why different turntables do not produce the same results, despite the fact they spin at the same speeds, it should not be too great a surprise when our digital systems produce unique sonic signatures.

So the question I would next ask myself is this: what’s the best storage and delivery system for me? And the answer is a tough one to give in clear form, because the truth is that none are perfect and all have their issues. For example, using a memory player like our own PWT narrows the differences between optical storage media and hard or soft drives to the point of near confusion. But the PWT can be bettered by the proper implementation of a soft drive in the right computer setup, and the opposite is easily true.

Here’s the bottom line: digital storage mediums, like their analog counterparts, are completely at the mercy of connected equipment to produce a final outcome. Thus, no blanket statement can be made unless it includes the entire chain. We all want the silver bullet: this drive sounds better than that drive but the truth is more elusive than that. The bullet does not exist alone in a vacuum.

We are getting set to release our first album and we are excited. But how shall we present the data to our customers so they might hear it in all its glory? Downloads? Specially mastered CD? DSD high resolution? SACD? DSD or PCM? You get the point. For some who have optimized their CD based systems, the answer is obvious. For others, who have managed to produce stunning results from their solid state drives and computers, their solution is different again.

Bottom line? We have to be open to producing media in enough formats that makes the choice to optimize performance an easy one for those of us that have grown comfortable for which is better. And so far, for me, the physical disc reigns supreme.