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Old 7th April 2012, 03:30 PM   #211
jitter is offline jitter  Netherlands
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Correction to my previous post: "bottom right" must of course be "bottom left".

The printing has also been sanded off the glue logic. I'm thinking this thing isn't as proprietary as has been assumed. If the DACs really are the DAC8580, their interface is already "compatible with right justified digital audio format" according to the datasheet. Wouldn't that just mean a SPDIF receiver that feeds the eight DAC's through some standard logic ICs?
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Last edited by jitter; 7th April 2012 at 03:43 PM.
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Old 7th April 2012, 03:51 PM   #212
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Quote:
Originally Posted by Telstar View Post
Well measurements of the octave have been done here:
http://www.nosminidac.nl/downloads/octavehificritic.pdf
The reported THD+N in that article is -60dB (page 10). That is NOT the 18 bit resolution claimed previously in the article, it is shy of 10 bit real resolution.
Another measurement is needed.
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Old 7th April 2012, 04:44 PM   #213
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Could the receiver be a TI DIR9001?
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Old 7th April 2012, 04:54 PM   #214
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Yes, that does indeed look to be what it is. Give-away is that pin22 is the PLL filter connection and the datasheet shows it should go to a 680R resistor. That is precisely where it goes in your pic.
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Old 7th April 2012, 04:54 PM   #215
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Quote:
Originally Posted by abraxalito View Post
No, I don't think you've overlooked something - at least not in this respect I found a few inconsistencies with Martin Colloms' technical report (which I'll expound on if there's interest). As he doesn't talk about how he determined the alleged 18bits, I remain unconvinced of his conclusion. I think he might have been estimating the overall linearity of the DACs themselves - so my take is that he guesstimated their DNL (combined) was around the 18 bit level, meaning 0.25LSB DNL. I'm open to other offers for the 18bit claim. Its not really very easy to estimate the number of bits a DAC has purely from the measurements he's shown there.

Oh I just had a thought as I am writing this - perhaps the poor FFT plot represents quantizing distortion due to incorrect dither applied to his test waveform. Given that he's estimated 18bits, his test signal could have been dithered at the 18bit level resulting in that plot. Plausible?
I concur, that seems plausible to me as well. I think he did say, "about" 18-bits, which could also be about, 17-bits, or maybe, even about 16-bits, I suppose.

It makes sense that Metrum would utilize the DAC8580 over the DAC8581. The 8580 features a normal 3-wire audio input port, while the 8581 features a port which does not facilitate digital audio signals.
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Last edited by Ken Newton; 7th April 2012 at 05:11 PM.
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Old 7th April 2012, 05:57 PM   #216
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Hi,

Quote:
Originally Posted by abraxalito View Post
I found a few inconsistencies with Martin Colloms' technical report (which I'll expound on if there's interest).
I think you should.

I also noticed a few things, but being in the industry and all I think I should avoid comments in public...

Ciao T
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Old 7th April 2012, 07:09 PM   #217
jitter is offline jitter  Netherlands
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OK, my PC-DSO isn't any good at measuring very low level signals or precise frequency responses, for that I refer you to the Hifi Critic review.
Much more interesting, though, are how sinewaves look through a NOS DAC. No doubt it's what has kept so many from taking NOS seriously and still do for those that haven't heard it. And itīs those measurements you donīt find in reviews.

I used a Micromega DAC1 to get the result from a "conventional" DAC. This DAC isn't capable of 96 kHz sampling frequency, so only the results for 44k1 are given. I measured the Octave at 44k1 and 96 kHz to show the difference.

The pictures are from left to right:
Octave, 44.1 kHz, 1 kHz sine;
Octave, 96 kHz, 1 kHz sine;
DAC1, 44.1 kHz, 1 kHz sine;
Octave, 44.1 kHz, 5 kHz sine;
Octave, 96 kHz, 5 kHz sine;
DAC1, 44.1 kHz, 5 kHz sine;
Octave, 44.1 kHz, 20 kHz sine;
Octave, 96 kHz, 20 kHz sine;
DAC1, 44.1 kHz, 20 kHz sine.
Attached Images
File Type: gif oct_1k_dso_44k.gif (4.8 KB, 256 views)
File Type: gif oct_1k_dso_96k.gif (4.8 KB, 247 views)
File Type: gif dac1_1k_dso_44k.gif (4.7 KB, 210 views)
File Type: gif oct_5k_dso_44k.gif (5.4 KB, 36 views)
File Type: gif oct_5k_dso_96k.gif (5.4 KB, 36 views)
File Type: gif dac1_5k_dso_44k.gif (5.3 KB, 34 views)
File Type: gif oct_20k_dso_44k.gif (7.6 KB, 32 views)
File Type: gif oct_20k_dso_96k.gif (8.0 KB, 29 views)
File Type: gif dac1_20k_dso_44k.gif (7.3 KB, 27 views)

Last edited by jitter; 7th April 2012 at 07:29 PM.
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Old 7th April 2012, 07:28 PM   #218
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I also did some spectrum analysis with the same variations as my previous post, again from left to right:

Octave, 44.1 kHz, white noise;
Octave, 96 kHz, white noise;
DAC1, 44.1 kHz, white noise;
Octave, 44.1 kHz, spectrum of 20 kHz sine;
Octave, 96 kHz, spectrum of 20 kHz sine;
DAC1, 44.1 kHz, spectrum of 20 kHz sine;

Clearly visible are the images in the NOS DAC.

If you ask me if I can hear any of the really distorted looking signals coming out of the Octave the answer is a very firm NO, I don't. Given that these distortions are caused by frequency components outside the audible band, I'm not at all surprised that I really don't hear them, simply because I can't. As I wrote before: the perfect low pass filter is already in us!
Attached Images
File Type: gif oct_wn_fft_44k.gif (6.0 KB, 32 views)
File Type: gif oct_wn_fft_96k.gif (5.7 KB, 20 views)
File Type: gif dac1_wn_fft_44k.gif (5.7 KB, 18 views)
File Type: gif oct_20k_fft_44k.gif (7.8 KB, 22 views)
File Type: gif oct_20k_fft_96k.gif (7.5 KB, 17 views)
File Type: gif dac1_20k_fft_44k.gif (5.6 KB, 18 views)

Last edited by jitter; 7th April 2012 at 07:32 PM.
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Old 7th April 2012, 07:32 PM   #219
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Do you think it does even hold a candle to DAC1?
To me, the 5kHz @ 44.1kHz one looks like is a 4 bit sinusoide... Those distortions are not outside the audio band, I bet that using some headphones you could hear the difference.
I am very interested in a mix of 19+20kHz 1:1 - for both of them.

Last edited by SoNic_real_one; 7th April 2012 at 07:34 PM.
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Old 7th April 2012, 08:07 PM   #220
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Whether or not this is relevant I don't know. But I'm interested in seeing what the spectrum looks like at low frequencies when replaying the 20kHz sine. We've got what the spectrum looks like above it, but not below, does stuff fold back into the audio band.

Of course if you show the 19+20kHz tone we will get to see what it looks like down low anyway as the product of the IMD test.
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