New Xiph.Org video: "Digital Show & Tell"

[xiphmont]

Hi all, some amount of (strictly non-commercial) organizational self-promotion here:
Xiph.Org's Episode 2: Digital Show and Tell is out!

This one is aimed squarely at some of the most fundamental questions and misconceptions that technically oriented people tend to have about digital audio. It's a followup to last year's "Why 24/192 Music Downloads Are Very Silly Indeed" based on the email we got in response to the article. It should be considerably less controversial (I hope) as it's all basic facts that can be checked easily using a DAC, a scope, and a spectrum analyzer. Rather than rely on math and lengthy explanations, the goal here is simply to show reality in action.

I hope folks enjoy it!

 

[Ethan Winer]

Excellent job. Repeat after me: "Digital audio doesn't really contain steps."

--Ethan

 

[audioguy]

Lot of folks (WBF posters and others) are going to try to pick apart that document. I found it very enlightening.

 

[Johnny Vinyl]

Lot of folks (WBF posters and others) are going to try to pick apart that document. I found it very enlightening.

Let the games begin!

 

[Bruce B]

Excellent job. Repeat after me: "Digital audio doesn't really contain steps."
--Ethan

Shawn Britton – Senior Mastering Engineer at Mobile Fidelity Sound Labs
“One of the reasons by Mobile Fidelity is doing vinyl again, analog if you prefer, is that analog, it’s continuous. If you look at a sine wave, it’s a continuous wave. Whereas digital is an approximation, or a subset, of the analog waveform, it’s sampled, it’s steps, so you don’t get the full information. The resolution is not there. So with vinyl, even to neophytes, it’s immediately apparent the sound quality is so much better with vinyl.”

 

[Daveski]

Thank you xiphmont. I enjoyed it. It's obvious someone invested much time and effort in producing it. Well done.

 

[xiphmont]

Whereas digital is an approximation, or a subset, of the analog waveform, it’s sampled, it’s steps, so you don’t get the full information. The resolution is not there. So with vinyl, even to neophytes, it’s immediately apparent the sound quality is so much better with vinyl.”

Right. He's very simply wrong, and that's likely because he's going on the word of someone else that he trusts and respects.... who was also very simply wrong. That's part of the point of making videos like this-- to break the cycle of endlessly repeated myths.

Thanks everyone for the kind reviews.

 

[Ethan Winer]

He's very simply wrong ... That's part of the point of making videos like this-- to break the cycle of endlessly repeated myths.

Exactly. Misinformation become even more dangerous when people who are successful and highly respected experts in some other aspect of audio make statements about things they don't understand. Then people who don't know how to tell what's real or fiction for themselves only have "reputation" to go by as they pick a side for who to believe. As your article explains, it's drop dead trivial to prove that digital audio does not have steps. You'd think people would read that, and see the 'scope photos, and that would be the end of it. But no...

--Ethan

 

[Bruce B]

You know what I hate?

When you want to watch a video and the format will not allow you. You need to download more crap on your computer or have proprietary software that you will never ever use again. Oh well....

 

[Mike Lavigne]

Excellent job. Repeat after me: "Digital audio doesn't really contain steps."

--Ethan

no steps?.....i call it listening to gaps in the music.

the problem is not the steps, it's the gaps between them.

 

[xiphmont]

You know what I hate?
When you want to watch a video and the format will not allow you. You need to download more crap on your computer or have proprietary software that you will never ever use again. Oh well....

We only released in free codecs. h264 is proprietary. MPEG-LA will not sell us a license to legally use it.

FWIW, the Web had a universally accessible format mostly settled, and then Apple blew things up with a closed format they just happened to partly own. Then Microsoft signed onto the Apple bandwagon. I'm pissed about it too. Fortunately, Safari and IE combined are a rather small minority of market share today, so we really don't have to care much about them. <-- I'm saying this absolutely dripping with irony as a Linux user

[edit: sorry Bruce, that came of squarely misdirected at you. It is the unfocused frustration/butthurt of an entire generation of *nix users]

 

[xiphmont]

no steps?.....i call it listening to gaps in the music.

the problem is not the steps, it's the gaps between them.

Hmm, don't see those on the scope either. Maybe I needed something faster than 100MHz.

 

[jmvalin]

no steps?.....i call it listening to gaps in the music.

the problem is not the steps, it's the gaps between them.

Well, let's just hope these gaps are no worse than the gaps between magnetic particles on tape... or between vinyl molecules ;-)

 

[rbbert]

Shawn Britton – Senior Mastering Engineer at Mobile Fidelity Sound Labs
“One of the reasons by Mobile Fidelity is doing vinyl again, analog if you prefer, is that analog, it’s continuous. If you look at a sine wave, it’s a continuous wave. Whereas digital is an approximation, or a subset, of the analog waveform, it’s sampled, it’s steps, so you don’t get the full information. The resolution is not there. So with vinyl, even to neophytes, it’s immediately apparent the sound quality is so much better with vinyl.”

no steps?.....i call it listening to gaps in the music.

the problem is not the steps, it's the gaps between them.

These are such old, tired and specious arguments about why digitally stored and analog stored music sound different. It's SO much more likely that it has to do with filtering (both A>D and D>A) and perhaps the actual mechanism of the conversions. Just think about the differences between DSD and PCM, for example. And what about the Audio Note DAC, which doesn't even have a reconstruction filter, so the output really IS a "series of steps", but which (by most reports; I haven't seen one myself, much less heard it) sounds excellent.

 

[xiphmont]

so the output really IS a "series of steps", but which (by most reports; I haven't seen one myself, much less heard it) sounds excellent.

I've tested a couple examples of DACs that resample to push the reconstruction noise to 100kHz or higher and simply dispense with the output filter. They sound just fine, but unless you're careful, you're going to blow your amp or tweeters with them if there's no lowpass downstream. They have as much or more power sitting up in the low RF than they put out in the audible band.

Even low-end Sigma Deltas are dispensing with AA filters these days as a cost-cutting maneuver. It's still not a stairstep since the line output stages fall off before 2MHz or so. They just look real fuzzy on a scope.

[edit: Hm, I wonder how that interacts with slew rate limitations in Big amps. I never though to test that.]

 

[rbbert]

AFAIK, the Audio Note doesn't resample or oversample

 

[xiphmont]

AFAIK, the Audio Note doesn't resample or oversample

ballsy. I have to wonder just true the 'no AA filter' is. No explicit/discrete filter, with an output stage tuned to roll off hard I'd believe, but that + no oversample is still kind of remarkable. I'll have to look around to see if I can find one to bench.

 

[rbbert]

John Atkinson tested it for Stereophile recently

 

[xiphmont]

John Atkinson tested it for Stereophile recently

Thanks, found it. They have, indeed, 'made the stairsteps real'. That probably wouldn't even be that horrifying if the distortion/clock jitter levels weren't so high. "the Audio Note's lack of a reconstruction filter allowed the negative-frequency image energy to play havoc with the spectrum" [where the 'negative-frequencies' he refers to is the aliased image].

And yet, reviewers liked the sound (and I don't doubt they did). Maybe Ethan needs to revise upward his levels of acceptable noise and distortion products in digital signals After all, it wasn't so long ago that most DACs put the AA filter transition band on the aliasing side of Nyquist.

 

[mep]

I think one of the reasons people think that digital creates stair steps is because in the recording stage, it does as you have shown. However, when it goes back to an analog signal after it has been converted by the analog output stage, it's a continuous sine wave. The fact remains it is a stair step when recorded. I also think that showing a 1 kHz sine wave after it has been recorded might just be misleading because music is never just a 1 kHz sine wave. I think it would be better to show screen shots of full frequency music being recorded digitally and show what it looked like on the scope prior to D/A conversion and what it looked like on another scope after it came out of the D/A converter to show how closely it resembled the input signal. I don't think that showing a pure 1 kHz sine wave going through the D/A conversion is telling the whole story.