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Old 8th September 2003, 06:03 PM   #1
A 8 is offline A 8  Sweden
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Default Just curious...-100dB dithered 16 bit?

Who of you, using what, have tested and was able to clearly hear the -100dB dithered 16 bit 1001Hz sinus signal throught your cd based system?
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Old 8th September 2003, 07:25 PM   #2
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I've done some listening with a single bit signal on a crystal evaluation board with LT1028 opamps driving a Grado headphone.. allthough barely visable on scope it was clearly audiable..

But this is probably not you you mean.

Could you explain the -100dB dithered part of your question?

Regards,
Thijs
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Old 9th September 2003, 01:30 AM   #3
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With a 16bit digital number, the maximum resolution that can be acheived is -96.32dB (n[bits] * 6.02 = x[dB]). Dither is applied in A/D converters and D/A converters to get rid of noise. Dither can be applied in a variety of patterns and is almost always only the random generation of the LSB only. But it is impossible to measure or hear a difference on a 16 bit number at -100dB.

And if you were trying to generate a 1kHz signal at -100dB on a 16bit system you would never actually hear the tone (assuming the same reference of 0dB) because its not capable of producing it. You would just hear pink/white noise that is created by the LSB dither sequence. If you had, say an 18/20 bit system (HDCD for instance), it may be possible with an extremely well designed analog and power supply back end.
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Old 9th September 2003, 01:54 AM   #4
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Quote:
Originally posted by Tieftoener
With a 16bit digital number, the maximum resolution that can be acheived is -96.32dB (n[bits] * 6.02 = x[dB]). Dither is applied in A/D converters and D/A converters to get rid of noise. Dither can be applied in a variety of patterns and is almost always only the random generation of the LSB only. But it is impossible to measure or hear a difference on a 16 bit number at -100dB.
No, it's quite possible.

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And if you were trying to generate a 1kHz signal at -100dB on a 16bit system you would never actually hear the tone (assuming the same reference of 0dB) because its not capable of producing it.
Sure you would, and yes it is.

Quote:
You would just hear pink/white noise that is created by the LSB dither sequence.
No, you'd hear it alright. And it can be measured as well.

The -100dB sinewave gets added to the dither noise and thus results in a greater amount of energy at 1kHz. Because of the way our ears average sound, we can hear quite a ways below the noise floor. Particularly when pure tones are involved.

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If you had, say an 18/20 bit system (HDCD for instance), it may be possible with an extremely well designed analog and power supply back end.
Wouldn't need that at all.

se
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Old 9th September 2003, 01:59 AM   #5
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Quote:
Originally posted by tschrama
Could you explain the -100dB dithered part of your question?
He means that a dithered 16-bit system was used to encode a sinewave that was at -100dBFS.

se
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Old 9th September 2003, 04:27 AM   #6
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In the name of trial and error....

I just generated a 1001Hz tone using a tone generator program. I noticed there was a bunch of noise in the signal.... So, I EQ'd all out everything to -60dB (except the 1KHz band) in Goldwave and was left with a pretty impressively noiseless sine wave. I put this to full scale 16bit wave file. I tried to scale it down using the volume function in Goldwave, but it has a lower limit ratio of 0.01... and for -100dB we need 0.00001

So, I found the function expression calculator - I multiplied the signal by 0.00001... thus resulting in a -100dB wave file of 16bit resolution.

I wasn't even going to bother, but I did try playing it through my Klipsch Promedia speakers and SB Live! card... I know, I know - as I said, I wasn't expecting anything. The noise this POS soundcard created when generating the pure sine tone is enough to gag a horse. Good thing I thought of putting the signal through the equalizer function first...

Because its late and I (unfortunately) have to go to work in the early AM, I'm going to hold off on playing this through my "high resolution" system. I will burn the file to a CD tomorrow night and try it out.

In the mean time, besides telling me I'm wrong, can you give a basis (other than the ear can hear below a noise floor) for my ineptitude? Weather or not the ear can hear below it (which I agree to) doesn't mean the system can generate it... Again, I'm wrong or whatever, and that's fine - I just need some reasons so I can understand and correct myself.

Thanks, and Ta Ta For Now...
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Old 9th September 2003, 05:42 AM   #7
Werner is offline Werner  Europe
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Quote:
Originally posted by Tieftoener

So, I found the function expression calculator - I multiplied the signal by 0.00001... thus resulting in a -100dB wave file of 16bit resolution.
Making more than a few assumptions about how Goldwave handles the requantization, not?

Try attached file collection for a demo, it is Chris Hicks' classic dither demo from 1995.

Part 1 ...
Attached Files
File Type: zip round2.zip (18.1 KB, 30 views)
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Old 9th September 2003, 05:44 AM   #8
Werner is offline Werner  Europe
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Default Hicks' dither demo

Part two ...
Attached Files
File Type: zip dith2.zip (92.6 KB, 25 views)
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Old 9th September 2003, 05:51 AM   #9
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Quote:
Originally posted by Tieftoener
In the mean time, besides telling me I'm wrong, can you give a basis (other than the ear can hear below a noise floor) for my ineptitude? Weather or not the ear can hear below it (which I agree to) doesn't mean the system can generate it... Again, I'm wrong or whatever, and that's fine - I just need some reasons so I can understand and correct myself.
As I said, the energy of that -100dBFS sinewave gets added to the energy of the noise used for dithering.

Let's say you dither with white noise which has equal energy per Hertz. In other words, every frequency component of the noise has the same energy. Now you add your 1kHz sinewave and the energy at 1kHz is greater than it was before. And that additional energy gets encoded in the A/D process along with the noise.

So if all you encode is dither with no signal and take a look at it averaged out in an FFT plot, you'll just see a bunch of grass at the same level. Look at it again with the -100dBFS 1kHz sinewave and then you'll see a little spike sticking up above the grass at 1kHz.

Because our ears average over time just as an averaging FFT does, we can also detect that additional energy at 1kHz provided it's not too far down in the noise.

This help?

se
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Old 9th September 2003, 08:39 AM   #10
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Thanks!

I understand, (at least I think I do) ....

... so this dithering is adding noise before going to ADC and.... The noise must be 'loud' enough cross the LSB value ... say 50% of the time for maximum effecientcy of this dithering process?....

A tiny sinus signal added to this noise will change the occurence of the crossing of the LSB ... this happens in a patern... the pattern is the added sinewave...


I think this could be made audioble, and on an averaging osciloscope also visible....

This reminds me a bit of a process called Stochastic-resonance. A theory to explain the capability of human hearing to function so well in negative S/N eviroments...


Regards,
Thijs
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