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In Reply to: Re: I looked at the 777 review... posted by Frank on January 30, 2003 at 13:16:17:
For the regular CD player, the noise at 10 kHz is about 10 dB higher with signal compared to without signal.Maybe they put the signal generator too close to the player- who knows.
It's got nothing to do with DSD or the noise being modulated by the signal.
Follow Ups:
from a signalgenerator next to the player.The rise for the cd signal is less severe than the sacd's modulation but it indicates 1 bit dac technology is used.
The signal modulates the noise there's no doubt about it.
see link. I wonder if you could find any CD player of any design that does not.
"This is due to the high-order noise-shaping used in the Crystal delta-sigma DAC to achieve as high a resolution as possible below that frequency. "It's evidence of 1 bit dac technology and noise shaping
it can be found in the latest Stereophile, in the review of the Ayre D1 DVD/CD player. The plot for the spectrum given the dithered 1 kHz signal is substantially identical to that of the Meridian 508.24. It rises to -108 dB at 10 kHz.They say in the write-up that the noise floor in this graph is the same as the noise floor of the dither in the input signal.
That is your answer. This has nothing to do with noise shaping. They are inputting a signal with a rising noise floor, so that is what they are getting at their output.
This is why all the Stereophile graphs of this test output look pretty much the same.
Certainly, the noise shaper is not moving any signal energy. Nothing of the sort happens.
Normal dither will have the effect that the noisefloor rises across the entire bandwith and with a signal a 1.5..3dB rise should occur.With dsd and noiseshaping you see the rise in noise only above a certain frequency.
Yes, the graphs are generated by a dithered 1 kHz signal. Yes, they all look similar. No, they're not all the same and in fact they can differ considerably. It is the differences in the noise floor at various frequencies that JA draws attention to: they are significant. Frank is right about one thing: noise-shaping leads to a much steeper slope.
this has kind of gotten off on a tangent. The behavior Frank noticed led him to conclude that SACD noise shaping also shapes the signal. I pointed out that the same behavior occurs on CD player graphs. He said this was also due to noise shaping.Well I looked at these output charts for about 5 different CD players. They had slightly different wiggles in slightly different places. But they were all basically the same shape. And then I read the text in the latest issue.
It is very obvious that the change in the noise floor between "digital black" and the dithered signal is primarily due to the noise floor in the input signal due to the dither. It has nothing to do with whether the DAC is single bit or not.
OK this applies to CD players. Now we all know that there is a noise floor that increases in SACD and it appears in the Stereophile graphs to increase rapidly above 8 kHz. This is part of the design.
It is still not the case that the noise shaping shapes the signal. Frank's logic, which was not true for CD, is no more true for SACD.
To test sacd performance with a 1kHz dithered testtone as dsd signal is not logical as dsd should be able to cope with an -90dB testtone at 1kHz on it's own. If dither on a -90dB testtone is needed for good testresults with dsd then sacd would be in big trouble.I think the dither is applied to the 16bit pcm test signal.
And of course the noise is in the dsd signal. And my point is that the dsd noisefloor in that signal is modulated by the signal.
The digital black is just a dsd signal with a signal just high enough to keep the muting circuitry from activating. In effect this is the bottom noise floor of dsd (on that partical player).The question is where the test signal is derived from. From a signalgenerator with noise in it's output or is it a math derived 'ideal' testsignal. In the latter case the noise level should be the same as the bottom noise curve.
If it's from a signal generator the rise in noise level should be the same on different machines asuming the same test disc is used.
Frank,
I'm pretty sure it is the same test signal JA uses for the linearity test.
Except that the SACD players clearly show less dynamic range than CD players above 10 kHz or so, and that clearly is a result of noise shaping - as JA has often remarked. The question remains: why does the increase in the noise floor show up an octave below the ultrasonic level?
is too low to realize the promised specs.The rise in noisefloor is just showing that the noise shaper is becoming less effective beyond a certain frequency.
It also shows that distortion rises and that resolution is dropping.
As I said I still don't understand how these tests relate to the stated specs of the SACD players. They seem to be a lot worse than would be expected. But I need to look into what the specs really say-it is hard to believe that Sony would quote specs that are so completely out of line with test results (or that Stereophile would not note this discrepancy). I'll try to figure this out. To tell the truth, I've never paid much attention to their graphs until now.
Firstly, as JA has pointed out, very few Hi Rez players can deliver even 18 bits of resolution across the audible spectrum. Secondly, that SACD's resolution and dynamic range is frequency dependent in a way that Sony would rather not discuss. However, this may have no subjective consequences (again according to JA).
I've been digging around the Stereophile charts and the Sony specs. The spec for the SCD-1 is 105 dB dynamic range in the audio band, presumably up to 20 kHz. So I looked at the review of the SCD-1 and here is the link to the graph, not with a 1 kHz digital signal but with digital silence. This shows the rising noise characteristic, but it also shows that it stays below 105 dB all the way up to 20 kHz. It is just below this at 20 kHz. Seems to me this is the way the noise spectrum is designed to look. This would agree with the spec.OK, why does the 777 graph not look like this? I would think it should. I would think that machine is operating out of spec and should be repaired. I don't think the noise is designed to be as high as that shown in the graph.
My assumption would be that the 1 kHz dithered tone is a tougher test, and more indicative of actual resolution.
it's nice to see someone taking the time to establish facts rather than conjecture
input, and have nothing to do with the components being tested. JA is paid by the square foot, so he just keeps printing the same graph.
it's not that funny anymore, and not very becoming either
This is also why Meridian changed over to Analog Devices Multi-bit Delta Sigma Architecture DACs in the 5xx and 8xx series.Regards,
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