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Why digital seems to be affected by power and cables

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I'm intrigued how digital transports seem to be affected by power and cables in a way, that to my ear, sounds like an analogue effect.

 

For example, Nordost are known to sound on the 'bright' side. I bought a Nordost power cable for the Apple TV, and it sounds bright! Very bright (compared to the stock cable). Yet the Apple TV is outputting 1s and 0s into an optical splitter which is outputting 1s and 0s into a DAC. If everything is 1s and 0s how can a cable effectively change the frequency response of what we are hearing?

 

I've found that HDMI cables, optical cables, coax cables, and USB cables all have a similar effect.

 

If the change is so audible, why hasn't anyone been able to describe the mechanism and why is it still common to hear statements about it's just 1s and 0s?

 

My guess is that no one has bothered to look for the difference. I don't think there is some unusual psychoacoustic effect or unusual quantum mechanism.

 

One possibility I would like to throw out there is that digital signals might be more like analogue than we realise.

 

A basic 16 bit stereo signal consists of two 16 bit PCM words. High frequencies rarely use full amplitude, otherwise they'd blow the tweeters. So a high amplitude high frequency signal might only affect the last 4 bits:

 

0000000000001111

 

Lower frequencies, or passages where there is a lot of music, will have a much higher amplitude, in this case they can affect all of the bits:

 

1111111111111111

 

Every 16 bit word will have different numbers, but quieter passages will have less changing bits, than the louder passages. 

 

I'm wondering whether the increase in number of bits changing per word in louder passages creates a higher current draw on the power supply than quieter passages, just like analogue?

 

In addition it's possible that the digital signal could have frequency components. If we take a low frequency signal that is decreasing in volume slowly over time:

 

0000000011111111

0000000011111110

0000000011111101

0000000011111100

0000000011111011

0000000011111001

0000000011111000

 

We can see that a good portion of the signal isn't changing between samples. I'm speculating that it effectively has a low frequency component, the left 13 bits, compared with the right 3 bits.

 

If a cable or power supply favoured certain frequencies, they could affect the amplitude of the digital signal. That amplitude change is effectively a kind of noise which could affect the receiving component, and the effect could be a kind of analogue change to the sound, e.g. woolly bass, increased high frequencies, etc.

 

I might be wrong, but the analogue impact on a digital signal might be much simpler than we think. Louder passages require more current, and audio frequencies have an analogous representation in the digital form.

 

Note that I'm not saying that analogue and digital are identical, there just might be more direct parallels than we realise.

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Just to see whether there is some merit to what I am saying, I wrote a simple program that counts the number of times a 1 changes to a 0 and vice versa. Note that the program has no knowledge that the 16 bit data represents a pulse code amplitude, it is just counting the change from 1 to 0 and back.

 

The first graph is the wave form of the original file (Jesse Cook's Mario Takes a Walk), about the first 2 seconds of the file:

 

post-105057-0-26168500-1448066175_thumb.

 

The second graph is the number of 1/0 changes per sample, averaged for every 1000 samples (I didn't want to load 200,000 samples into Excel):

 

post-105057-0-70025300-1448066448_thumb.

 

There is a fairly high correlation between the decoded PCM data and the encoded PCM data. If 1/0 changes correlate with power draw then the sorts of impact a power supply would make on an analogue component could be similar to a digital component.

 

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what we are hearing?.

 

It's experimenter bias - a.k.a. the placebo effect.

 

It's extremely powerful and has to be carefully designed out of any meaningful experiment.  (Along with volume changes)

 

That doesn't mean that you cannot hear something that the current engineering / audio community doesn't know is going on.  That's actually how we progress.   But you need to have an actual audible difference.

 

 

 

 

 

 

Note that I'm not saying that analogue and digital are identical, there just might be more direct parallels than we realise.

 

As a one-time digital designer, there certainly are.   And in the rush to "cheap" combined with "it's digital so it can't matter" means that basic, obvious stuff gets ignored (e.g. UDP is lossy, noise remains noise, clock and voltage control in DACS matters)

 

If you are at all interested in this stuff and want to understand then STOP SPECULATING and go and READ.  There's a huge range of things that could make a difference:  it took nearly 20 years to sort out the CD player and industry is still arguing the finer points. 

Edited by thoglette

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 I've realised that leaves the non JAES subscribers in a bit of a pickle.

 

There are a some good articles out there but finding them can be a challenge amongst the snake oil and heavy maths. 

 

For example, http://www.tnt-audio.com/clinica/diginterf1_e.html 2004 talking about jitter

 

But I leave you with one thought from him

 

"In the average or low cost ones, these clocks oustanding pace would well be distorted and polluted by the not so cured clock path, by not correct matching, by the not perfect ground loops, the dirty power supplies, the low cost op-amps and so on.

 

In the most recent systems, in particular low cost DVD players, clock quality seems to be better than in CD players of just a few years ago. However, the sampling jitter remains rather high (500-600ps), and is essentially made of noise caused by digital or video circuits. "

 

I.e. the final quality achieve by an implementation of any architecture depends not just on what the architecture is theoretically capable of but also on skill and attention to detail when implementing it: the components used and the skill in PCB/case layout and noise management.

 

If you are at all interested in this stuff and want to understand then STOP SPECULATING and go and READ.  There's a huge range of things that could make a difference:  it took nearly 20 years to sort out the CD player and industry is still arguing the finer points.

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My guess is that no one has bothered to look

 

You'd be very wrong ;)

 

 

One possibility I would like to throw out there is that digital signals might be more like analogue than we realise.

 

All electrical signals are analogue.     It is only the encoding of the information which is digital.   

 

 

 

If you are at all interested in this stuff and want to understand then STOP SPECULATING and go and READ.

 

+1

 

These topics are very well understood.   There isn't anything (significant) that isn't already well explained, so no new theories are required.

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still arguing the finer points. 

 

It's an interesting aside .... I'm not so sure they are that much.    There's certainly usually "more than one way to skin a cat" of course, and that makes for debate ..... but "how it all works" is very well trodden.

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Just to be clear I am not talking about the quality of the signal with regards to jitter, noise, etc. I'm not trying to find a solution to improve the quality of digital.

What I am trying to understand is how a digital signal can be affected by a cable in a very similar way to an analogue signal.

Note that digital audio is encoded, therefore if a cable can affect certain frequencies it shouldn't have any impact on a digital signal because the digital signal isn't being transmitted by the same frequencies as the analog signal. In a very loose analogy it would be like comparing AM with FM.

However digital seems to be affected very similarly to analog. A case in point is that a bright sounding power cable makes a digital signal sound bright. How? Aren't all the 1s and 0s equivalent? How does the power cable know which 1s and 0s represent high frequencies and which represent low frequencies?

If someone can provide me with an article or book that explains the phenomenon I'm happy to read it.

I've never read anywhere how a digital PCM audio signal can be affected in a very similar way to an analog signal, with respect to power draw and frequency attenuation. The simplicity of my explanation is that the PCM signal is actually quite highly correlated to the analog signal. In contrast an encrypted PCM signal isn't.

But happy to be proven otherwise, feel free to provide links or criticise the theory.

Sent from my iPhone using Tapatalk

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Hehe.....the placebo effect.........I used to think that the most simplistic statement in hi-fi.........Now I'd actually say 'insulting'......

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Hehe.....the placebo effect.........I used to think that the most simplistic statement in hi-fi.........Now I'd actually say 'insulting'......

Please do explain.

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Guest Sime

Please do explain.

Agree, I don't get if he's for or against the placebo effect.

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The thing about placebo effect, cognitive bias and psychoacoustics is you won't even know it has taken affect on you when you enter into a room of various audio brand/models etc. The mind is a very powerful thing.

Edited by DefQon

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What I am trying to understand is how a digital signal can be affected by a cable in a very similar way to an analogue signal.

 

 

Unless your cable is busted, I'd say it can't

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Unless your cable is busted, I'd say it can't

 

C'mon, Trev ... everything affects the sound! :D

 

Andy

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This might stir up some discussion :)

 

Above I showed there could be a correlation between the power draw of a digital signal and the analogue signal.

 

But is there a correlation in the frequency spectrum?

 

The top image is the frequency spectrum of the decoded PCM of the same track above but about double the length (4.5 seconds). The bottom image is the frequency spectrum of the 1/0 transition counts:

 

post-105057-0-66205100-1448333567_thumb.

 

At first the bottom image looks like noise. But there are some slight dark vertical patches in the bottom image which correlate with the top image. More interesting is the lines at the very bottom of the image. These are probably around 500Hz right in the mid-range band. There is some correlation between those lines and the lines in the top image of the waveform. Any kind of constant frequency response between samples in the digital representation which is correlated to the original waveform is reasonably significant. It means that the digital signal will be attenuated in a very similar way to the analogue signal.

 

As I predicted in my first post, the most likely correlation would be in the lower frequencies.

 

So:

  • Am I seeing things? (placebo effect, experimenter bias)
  • Even if there is some frequency correlation, could we actually hear it on the other side of the DAC?

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C'mon, Trev ... everything affects the sound! :D

Andy

"Everything" includes expectation, right?

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  • Am I seeing things? (placebo effect, experimenter bias)

Absolutely.  Like end time devotees, if you look long enough for "signs" you'll find them. Everywhere.

 

You have two choices in experiment design:  qualitative or quantitative.  The latter is "I hypothise and here's a yes/no experiement".  The former is using observation and analysis to generate possible theories from data.   Which may then be tested quantitively.  Go read up on "grounded theory", particularly Prof. Kathy Charmaz.

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There's plenty of data there, I don't see why it can't be evaluated quantitatively.

Sent from my iPhone using Tapatalk

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I'm intrigued how digital transports seem to be affected by power and cables in a way, that to my ear, sounds like an analogue effect.

For example, Nordost are known to sound on the 'bright' side. I bought a Nordost power cable for the Apple TV, and it sounds bright! Very bright (compared to the stock cable). Yet the Apple TV is outputting 1s and 0s into an optical splitter which is outputting 1s and 0s into a DAC. If everything is 1s and 0s how can a cable effectively change the frequency response of what we are hearing?

I've found that HDMI cables, optical cables, coax cables, and USB cables all have a similar effect.

If the change is so audible, why hasn't anyone been able to describe the mechanism and why is it still common to hear statements about it's just 1s and 0s?

My guess is that no one has bothered to look for the difference. I don't think there is some unusual psychoacoustic effect or unusual quantum mechanism.

Hi

Full credit for taking such an effort with the data so far...

Going back to your original example of the Nordost power cable sounding bright, how much of your perception was bias?

If you can statistically tell the difference reliably in a blind test (single blind as a start), then you may be on to something.

Swapping a power cable yourself and hearing a big difference is way to prone to bias.

I had bias demonstrated to me very clearly when I was swapping between MP3 and hi-res tracks on my setup - the difference was night and day until I handed the remote to someone else - I couldn't reliably pick the difference

----------------

.

Edit - iPad

Edited by almikel

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Above I showed there could be a correlation between the power draw of a digital signal and the analogue signal.

 

I didn't see where.

 

Any kind of constant frequency response between samples in the digital representation which is correlated to the original waveform is reasonably significant. It means that the digital signal will be attenuated in a very similar way to the analogue signal.

 

It is hard to guess what you actually mean by this, but I strongly suspect it doesn't mean what you think it means.

 

 

  • Am I seeing things? (placebo effect, experimenter bias)

 

The 'vertical lines', yes you are (seeing things)   .......   The horizontal / low frequencies, no.  There is very slightly higher power in the lowest frequencies .....  it could even be that there was a common cause of the noise  (but that is complete speculation).

 

 

Even if there is some frequency correlation, could we actually hear it on the other side of the DAC?

 

Maybe.

 

... BUT what you hear, will not be in anyway related to the first chart.     The effect of the 'noise' (if any) in the digital signal on the output of the DAC, will be completely unrelated distortion products.

 

 

There's plenty of data there

 

No there isn't.

Edited by davewantsmoore

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I didn't see where.

Post #2

Sent from my iPhone using Tapatalk

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I see.    The correlation is to be expected, but I suspect it doesn't mean what I think you think it means.

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Oops, I'd left this discussion for a few days and missed out on all the good stuff.

 

I've always heard differences between EVERYTHING. Any change in interconnects, speaker cables. power cables, AC filters, hi-fi racks, anti-vibration pads, speaker phase...... you name it. 

 

If you pay ANY attention at all to the sound that's coming out of you speakers, you can hear the differences. 

 

So anyone who uses the explanation of 'placebo' is......er..........how can I put this politely??  Misguided. There!

 

That's not to say that these changes, or 'upgrades', are necessarily better. In fact,  it's been my long experience that a good majority of 'tweaks' actually degrade sound quality. 

 

But that's another discussion! 

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So anyone who uses the explanation of 'placebo' is......er..........how can I put this politely??  Misguided. There!

 

 

So somehow audiophiles are immune to the cognitive biases (and particularly the placebo effect) which affect the rest of the population?  Wow! 

 

There's a Nobel prize in that one for you- if you can only prove it.   

Edited by thoglette

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Misguided. There!

 

Only a Sith talks in such absolutes.

 

Sure, I agree.....  it is misguided (and lazy) to suggest that placebo is responsible for something when no other investigation has been carried out on something....   but that is almost never the case.

 

 

Placebo, bias, and similar effects are extremely real, and well understood .....  and it is completely ludicrous to propose they don't exist for audio.     In fact if you do your own testing, it is really easy (and quite depressing) to discover just how prevalent they are ....   even for someone like me who is (was?) convinced they are impossible to fool and have gold-plated golden ears.

 

I went from everything matters, listening is everything ....... to almost the total opposite,  over 2 decades.    The key wisdom is using the right approach in the right situation.    Subjective tools (listening) is the only sensible way to choose between compromise A and compromise B  (like most consumers have to) ...   "this is the entertainment business"  (and there is no harm in it).       But on the other hand, people all too readily get this confused with quantification of objective things, where "listening" and subjectivity are regularly counter productive.

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