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Old 4th December 2012, 11:53 AM   #231
erin is offline erin  Australia
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Firstly I don't own the product nor make the product so don't get upset with me.

When archiving an LP, what sort of HF noise gets into the signal chain?

If I put my turntable on the scope and check for HF noise and cant see any, would it be safe to use this ADC?

Same thing in a studio, if I put my scope, or spectrum analyser on the mic-pre, and couldn't see any HF noise, would it be safe to use this ADC?
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Old 4th December 2012, 11:59 AM   #232
erin is offline erin  Australia
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Thinking about this some more, if you can only hear a tiny hiss from your speaker when the phono amp is on, then this means the hiss is at very low amplitude, any noise above the range of hearing is also likely to be at very low amplitude, even if this low amplitude HF noise was to create an alias, it also would only be at very low amplitude, and come out as low level "noise", I would not expect this to sound like a "birdie"
I don't see the problem!!
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Last edited by erin; 4th December 2012 at 12:02 PM.
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Old 4th December 2012, 12:07 PM   #233
SY is offline SY  United States
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Quote:
Originally Posted by erin View Post

When archiving an LP, what sort of HF noise gets into the signal chain?
The tracing noise along the groove, ticks, pops, any minor mistracking... if you use a spectrum analyzer to look at the HF content of a phono output (a scope is not the appropriate instrument), it's pretty significant.
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Old 4th December 2012, 12:10 PM   #234
erin is offline erin  Australia
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The tracing noise along the groove, ticks, pops, any minor mistracking... if you use a spectrum analyzer to look at the HF content of a phono output (a scope is not the appropriate instrument), it's pretty significant.
I did actually say spectrum analyser when referring to the mic pre. I just omitted to say so with reference to the phono amp. My bad.
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Originally Posted by erin View Post
Same thing in a studio, if I put my scope, or spectrum analyser on the mic-pre, and couldn't see any HF noise, would it be safe to use this ADC?
And for archiving an LP I would presume that a person would be locating a pristine copy, or de-clicking the track after the recording anyway.
And even if a person was to leave the "pop" on the recording the alias would only be of the "pop". In real life, I can't see the issue.
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Last edited by erin; 4th December 2012 at 12:14 PM.
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Old 4th December 2012, 12:54 PM   #235
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Quote:
Originally Posted by erin View Post
I did actually say spectrum analyser when referring to the mic pre. I just omitted to say so with reference to the phono amp. My bad.


And for archiving an LP I would presume that a person would be locating a pristine copy, or de-clicking the track after the recording anyway.
And even if a person was to leave the "pop" on the recording the alias would only be of the "pop". In real life, I can't see the issue.
pops and clicks have wide bandwidth well above the audible band !

you need to de-click the track before you sample it with an A-D and that means you need a filter to do this !!
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Old 4th December 2012, 01:23 PM   #236
Charles is offline Charles  Germany
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Originally Posted by Trevor White View Post
pops and clicks have wide bandwidth well above the audible band !

you need to de-click the track before you sample it with an A-D and that means you need a filter to do this !!
Hi Trevor,

thank you for your suggestion, but I think I have shown with the simple scopeshots on the Creation ADC website The Altmann Creation ADC, that a click, containing high bandwidth does indeed cause distotion when recorded with a sigma-delta ADC, but does not cause distortion when recorded with my ADC.

If you take a look at the scopeshots on my website, you will see.

A high frequency click or pop is not a problem for a filterless true ADC, so my initial question remains:

What is the only thing that causes really nasty and audible alias distortion when recording with a filterless SAR ADC even at 192kHz sample rate ?

Charles
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Old 4th December 2012, 01:42 PM   #237
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Hi Trevor,

thank you for your suggestion, but I think I have shown with the simple scopeshots on the Creation ADC website The Altmann Creation ADC, that a click, containing high bandwidth does indeed cause distotion when recorded with a sigma-delta ADC, but does not cause distortion when recorded with my ADC.

If you take a look at the scopeshots on my website, you will see.

A high frequency click or pop is not a problem for a filterless true ADC, so my initial question remains:

What is the only thing that causes really nasty and audible alias distortion when recording with a filterless SAR ADC even at 192kHz sample rate ?

Charles
You need to understand Fourier transform theory otherwise your arguments are totally unsound and are derived from false premises.

Also there are two pictures of oscilloscope displays and I can clearly see differences between the two so I don't know what you are try to demonstrate. Perhaps you should test your AD converter with a 20 KHz squarewave and see what happens
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Old 4th December 2012, 02:00 PM   #238
Charles is offline Charles  Germany
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Originally Posted by Trevor White View Post
You need to understand Fourier transform theory otherwise your arguments are totally unsound and are derived from false premises.

Also there are two pictures of oscilloscope displays and I can clearly see differences between the two so I don't know what you are try to demonstrate. Perhaps you should test your AD converter with a 20 KHz squarewave and see what happens
Hi Trevor,

I have shown that a sigma-delta ADC causes distortion when fed with a HF-click and that a zero-filter SAR ADC (i.e. my Creation ADC) does not create distortion, btw. the test wav I used is available for download on my website. So this is something everybody can try out himself and I need not add anything to pure facts, as they stand for themselves

In the examples on my websites I have chosen this mixed signal which contains a square step added to a sine wave, so that you can clearly see, that the step as well as the sine contains no distortion when recorded with my Creation ADC, but does get corrupted when recorded with any sigma-delta ADC

But your idea of sampling a 20kHz square wave is good. I have the DAC that can play back a true square-wave and I have the ADC that can sample a true square wave, and the output will again be a pure square wave.

Try this with a sigma-delta ADC/DAC and you will get a huge amount of distortion. To say that this distortion can be explained by the theory of Fourier transformation will not remove the distortion.

The definition of distortion is that the output is different than the input.

Charles
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Old 4th December 2012, 02:05 PM   #239
Julf is offline Julf  Europe
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Charles,

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Originally Posted by Charles View Post
I have shown that a sigma-delta ADC causes distortion when fed with a HF-click and that a zero-filter SAR ADC (i.e. my Creation ADC) does not create distortion
No, you haven't. You have shown that your creation doesn't seem to cause such gross distortion that it is visible with the bare eye on a waveform display on a scope. It is a totally meaningless measurement, unless your distortion is really gross (as in several %), and as long as the difference you are trying to show is in the amplitude (and not frequency/temporal) domain.

Could you show some spectrum plots instead - at last that would have *some* relevance?
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Old 4th December 2012, 02:10 PM   #240
Charles is offline Charles  Germany
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Originally Posted by Julf View Post
Charles,
No, you haven't. You have shown that your creation doesn't seem to cause such gross distortion that it is visible with the bare eye on a waveform display on a scope. It is a totally meaningless measurement, unless your distortion is really gross (as in several %), and as long as the difference you are trying to show is in the amplitude (and not frequency/temporal) domain.

Could you show some spectrum plots instead - at last that would have *some* relevance?
Hi Julf,

then I have at least shown that really gross distortion does appear with a sigma-delta ADC, and you can do the same test if you have an oscilloscope.

Charles
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