Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

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RE: Digital improving -final

Posted by Thorsten (M) on April 14, 2016 at 02:37:51

In Reply to: RE: Digital improving -final posted by J. Phelan on April 13, 2016 at 11:06:04:

Hi,

> One, CDs, as manufactured, were far from perfect.
> Hence the improvements heard by burning to CDR
> (gold ones were better) or using optical treatments
> (like Optrix).

Again, it is crucial to understand the how and why all these things make an impact.

> Hard-disk also made improvements over CD-drives.

Not really. Head over to the computer audio asylum if you don't believe me.

> All of these point to problems with read-in.
> More power supplies help, but the problem still persists.

Unless CD's are badly mangled, the "read-in" is bit-accurate.

The problem is crosstalk via power supplies. How do I know? I designed a CD-Player that was impervious to "burning CD's to CDR" and Optrix etc... And yes, the trick is power supplies - solely - separating power supplies as much as possible.

> Any modern-engineer working with magnetics will tell you they're
> not easy to shield !

Then these "any modern-engineer" should all be fired to the last man.

In the 1930's, 1940's, 1950's, 1960's, 1970's, 1980's and 1990's Magnetic components were easy to shield. In fact they still are as easy to shield today. I implemented shielded mains transformers in HiFi gear in the 2000's. It is not only possible, but also cheap, relatively speaking, but it is not free.

These days I work with magnetic components for high frequency power supplies and guess you what - they are also shielded, from the factory. Yes, they cost a few cent more than unshielded types, but they are readily available off the page.

> Feedback might very well be an issue -as reported by engineers
> working today. Ayre, DarTZeel and Hegel claim it and I believe it.

I have been using "non-nfb" circuitry for ages. Also circuitry with feedback. Both can be made to work well, you just have to understand the requirements of the circuit.

I will decline to comment on specific products or brands...

> And in these reviews, they discuss "downsampling". Do some reading.

I have. These reviews discuss using Asynchronous Sample Rate Conversion (ASRC), with the output sample rate set to or near 96kHz. And it is an old hat, a specific Pro-audio DAC resampled everything to 100kHz as of appx. 2005. Others like it were fairly common at the time, even in super cheap DAC's there was an ASRC. The manufacturers just forgot to claim downsampling as feature...

This may be because for CD standard Audio you get UPSAMPLING, not downsampling. Yes, with 176.4kHz and 192kHz you get downsampling - doing that if you have 768kHz capable DAC should probably be considered the same sort of thing as putting antifreeze into wine.

Personally I cannot say I am a great fan of ASRC and prefer any Audio Format to be rendered with as little digital processing as possible (which would be non).

Seems the UPSAMPLING/ASRC craze of the early 'oughties is doing a second coming, this time called DOWNSAMPLING, because by now we all know "upsampling = bad".

> Jitter creates -unwanted signals- in the chain

Generally Jitter does NOT create any direct signals that are independent of the actual signal. If you play digital silence there is no erroneous signal created by jitter. It creates increased noise with signal and added distortion, mostly of the IMD type.

> It was not "timing" -clocks are extremely accurate !!

Clocks of any kind have many imperfections. The ones commonly found even in so-called super-clocks are neither very accurate long term (this is called wander), short term (this is called jitter) or in an absolute sense (clock frequency), if compared (say) to a Stanford PRS-10.

> The "rounding errors" were discussed by American engineers,
> in several interviews.

This does not make it true or relevant.

If a digital filter is 24 Bit and it's design is competent (a supposition that I will agree may not automatically assumed to be true) the rounding errors will be in 24th bit, or, as no-one has made a 144dB dynamic range DAC in the DAC's noise-floor.

Even if someone made such a DAC, the rounding error would drown in microphone noise of the recording

> With many co. opting not to use "apodizing", they may be right.

Apodising, as I said refers simply to a filter with a cutoff lower than classic half-band. This kind of filter is a very british thing. The inventor, main proponents and/or main implementers are all british.

Apodising filters are currently available as standard only with DAC Chip's from one small british manufacturer. Any other implementation of such filtering would require bypassing the internal digital filter in the DAC Chip and performing the filtering externally in DSP.

Apodising was proposed by Peter G. Craven and for a specific reason. During recording the ADC typically includes a lowpass filter. Since the late 80's this filter is always digital and almost always a sharp rolloff half-band filter (AKA brickwall filter).

By using a lower filter cut-off during playback the playback filter will dominate the impulse response of the system and may be chosen to be very different to the recording filter, optimised for subjective performance. The downside, you loose a few kHz high frequency extension with CD Standard signals.

The benefits or not of apodising or not are indeed debated. I included apodising filters in one product I helped to design - I still prefer to avoid digital filters entirely and to use only analogue domain filtering instead (a british/japanese gig that few others have gotten in on, which does not make it invalid).

> Although it appears that many DACs were not reaching their
> potential, as you noted. But I replaced it with a new point.

I noted that some DAC Chips (very few) had THD & N with high signal levels that was substantially less than the CD Specification even though their noise levels (and/or -60dBFS Dynamic Range) is close to or matches CD Specification.

These kind of DAC Chips used to be very rare in quality equipment, though they had a bit of a renaissance due to publications in Musen to Jikken Magazine by Kusonoki San who showed the first modern "non-oversampling" DAC using these precise chips as "proof of concept".

Those who cannot really design but only copy have since been elevating these chip's in copies of Kusonoki San's designs (in my view incorrectly) to "high end" status.

Finally, please look at some early "Flagship" CD-Players and DAC's (mid to late 80's - say Sony DAS-R1 or Marantz CD/DA-12) and then tell me which of your claimed problems actually plague them and where they are materially worse than a modern CDP/DAC with your supposed improvements if playing 44.1kHz/16 bit material.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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