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Why do NOS dacs sound different to oversampling designs?

Opus111

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Non oversampling would be when the DAC chip is run purely at the native sample rate - for CD that's 44k1. This rules out use of any 'low-bit' DACs, so the DAC would need to be a native 16bit part to do justice to RBCD.
Treble droop is inherent to the DAC part because the reconstruction is done with a ZOH - zero order hold in pretty much all DAC designs. So even with oversampling there will always be some droop, its just a matter of degree and NOS gives the biggest droop.
Images don't 'fold back' that's only with aliasing, not imaging. Aliasing is for ADCs, imaging for DACs.
 

Phelonious Ponk

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You look to be misunderstanding the placebo effect - placebo effect differences most certainly are real. Just not reflected in the vibrations in the air.

Not really. They can appear to have a real effect - people may "feel" an improvement when taking a medical placebo, for example. That doesn't mean the placebo has affected a "real' change in their condition. It seems to run rampant in audio, where so many believe in the reality of things that have no real effect on anything but their beliefs. Here's a definition, for clarity: http://www.webmd.com/pain-management/what-is-the-placebo-effect.

tim
 

Opus111

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That doesn't mean the placebo has affected a "real' change in their condition.

Yet here is an example from your link :

For instance, in one study, people were given a placebo and told it was a stimulant. After taking the pill, their pulse rate sped up, their blood pressure increased, and their reaction speeds improved.

Not a "real" change in their condition? No, not really
 

amirm

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In audio, I don't think there is any lasting effect of Placebo. The reason is that it is a continuous experiment and should the bias change, so does the placebo. Let's say I get a new DAC and I think it is worlds better than the old. I sell the old and the new DAC becomes my main unit. The next day when I listen to it, it is no longer subject to the same placebo of it being a new DAC, and being compared to the old. So if the bias/placebo was defending the newness, then that effect is gone and you are back to something that may sound identical or even worse than what you replaced.
 

Ethan Winer

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The Zanden certainly measures differently.
Keith
I have no idea about any of these specific DACs! There may be real differences that are audible. But ears are generally much worse than test gear. For example, test gear can easily measure the difference between 0.003 and 0.005 percent distortion, but both are much softer than anyone could possibly hear. That's also much less than the distortion of any loudspeaker!
 

Ethan Winer

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You look to be misunderstanding the placebo effect - placebo effect differences most certainly are real. Just not reflected in the vibrations in the air.
I promise you I understand the placebo effect very well. :eek: But it's not real, and it always goes away in a proper blind test. So I ignore it when talking seriously about audio. :D

--Ethan
 

Opus111

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I promise you I understand the placebo effect very well. :eek:

I can see no reason to give any meaning to your 'promise'.

Plenty of my students claim to understand things but when I explore their understanding I find its deficient.
 

Phelonious Ponk

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Yet here is an example from your link :

For instance, in one study, people were given a placebo and told it was a stimulant. After taking the pill, their pulse rate sped up, their blood pressure increased, and their reaction speeds improved.

Not a "real" change in their condition? No, not really

I didn't say placebo can't have an effect, I said the perception of an effect doesn't mean the effect is real. And it doesn't. Yes the body can be driven to a measurable, physical reaction by the mind. What exactly is it your body does when you perceive an audiophile placebo? In the case of audio, surely placebo is all in your head, unless you think that believing you hear subsonic content changes your ears physically, allowing you to actually hear subsonic content. That would be an interesting hypothesis.

Tim
 

Opus111

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What exactly is it your body does when you perceive an audiophile placebo?

Produce endorphins? Seems to me subjectivists are all about getting off on the music, the emotional aspects.

In the case of audio, surely placebo is all in your head

So is all of reality so your distinction doesn't look to me to be meaningful. Go view the TED talk I linked to in the psychoacoustics area and educate yourself.
 

DonH56

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Note conventional DACs can be used with oversampled clocks, and there are delta-sigma architectures that do not require above-Nyquist clock rates, but usually when I see "NOS" in audio threads they are debating conventional DACs vs. delta-sigma DACs. Either design requires an anti-imaging filter at the output, both can generate glitches and such, but the delta-sigma designs have a rising noise response with frequency requiring (usually) a more complex filter.

A conventional DAC will have about 4 dB drop in frequency response at the Nyquist frequency due to the sin(x)/x output. That is a real effect. This may be compensated by a peaking filter (digital before or analog after the DAC, though digital gives up headroom), oversampling, using narrower pulses (which also reduces total output energy and typically reduces SNR), or some other means.

Input signals above Nyquist will be aliased in an ADC, but there is nothing in sampling theory to alias the output images from a DAC back into baseband. But, anything after the DAC may do so, whether due to some sort of electronic nonlinearity (mixing) in response to such HF energy, or a speaker that cannot respond to the HF energy and ends up with lower-frequency modulations on the output.

HTH - Don

p.s. I have a few DAC articles over on the WBF site, and of course there are a myriad of articles on the 'net and elsewhere by other industry experts (and some not-so-expert, of course).
 

amirm

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Thanks Don. Would be great to have a copy of those articles here. The forum software here is 100% compatible with what is there so all you need to do is hit "Edit" there, select all, copy and then paste into a thread here.
 

DonH56

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Unfortunately I'm working a ton lately (33 days in a row, couple of days off, now picking up again, blah). I assume the text is easy but I'd have to upload all the images again?
 

TBone

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Good OP question ... I've long wished to modify (lampi style) an old, not too used, cheap$ TDA1541 deck to compare to my resident player (w/1732 24/96 delta sigma design). So many existed, (I've owned a few early Phillips / Marantz versions prior), you'd think 'em easy to find ...
 

Opus111

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Put up some pics of the circuit board and I'll give you some suggestions for improvement.
 

TBone

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Put up some pics of the circuit board and I'll give you some suggestions for improvement.

I don't have one in my grubby hands yet, I'm looking (although probably not hard enough) for a local sale I can inspect. Searching for certain Philips models noted on the lampi site, would really luv a Marantz 94, in good shape, on the cheap. Thx for the offer, I'll keep it in mind if ever ...
 

Opus111

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The issue with Philips stuff (at least the ones I've owned) is they use the crummiest material for PCBs imaginable. Its not the industry standard FR4, presumably they save a few cents that way. You could also look for players which have PCM63s or PCM1702s, they'd also be worth modding. Another possibility is a Philips player with a TDA1543 (the bargain basement chip) or (better) a TDA1545.
 

TBone

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I've had a fair share of 1702 type players in my system, the most memorable being the orig SIM Eclipse and NOVA. Loved those players, but I certainly wouldn't consider modify em. I've budget ~$200 Canadian (about 13.98 us :rolleyes:) for a good but well taken care of used unit.

Truth be told. the very first CDP I had access, which I really played a bunch, was an early 1541 Philips design (forget which model), and it remains memorable (if my long term memory serves me well) simply because near every subsequent player ended up sitting idle in my system in comparison to my turntable, they sounded ... well ... too "digital".

So ... it's those fond memories that fuel this desire to own yet another old 1541 Philips.

Didn't know about the questionable PCB quality tho, is this an inherited problem with all/many of these old Phillips?
 

Opus111

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I don't know if its a problem in practice, just for modding I do prefer a robust PCB that holds up under multiple solderings and desolderings. Modding is tricky enough without poor materials distracting me...

A good example of a really robust PCB is in the Lite DAC-AH, that can be hacked about without major problems. I think Philips' PCB material is called 'SRBP' - paper based. Perhaps its used because its easier to drill.
 
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