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  • DonP
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Dynamic range question
Reply #75
This will probably add confusion to those already having trouble with bits vs dB, but here goes.

It turns out you can get that 96 dB range even with 1 bit samples IF you choose the percentage chance of rounding up (to 1) vs rounding down (to zero) to correspond with the signal voltage.  You do need a lot higher sampling frequency but less component precision and it turns out this is how many/most  DAC's work internally.

  • dhromed
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Dynamic range question
Reply #76
You can give it a try yourself.

These are music excerpts reduced to an equivalent of 4 bits (or slightly more, IIRC).


I'm completely surprised at how good these clips sound.

Apart from the unlistenable noise, of course. I'd expected there to be nothing left.

  • dhromed
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Dynamic range question
Reply #77
It turns out you can get that 96 dB range even with 1 bit samples IF you choose the percentage chance of rounding up (to 1) vs rounding down (to zero) to correspond with the signal voltage.


Isn't that exactly what pulse-density modulation is?

  • Woodinville
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Dynamic range question
Reply #78
I am sure that, if we would map a waveform into 4 bits and played that waveform back at 96 dB, everybody would hear it as a rather coarse sound, and if we would lover the sound to 15 dB (theoretically, not taking into account background noise ) that same coarseness would be significantly lower.


You can give it a try yourself.

These are music excerpts reduced to an equivalent of 4 bits (or slightly more, IIRC).


Undithered:

http://www.audiochrome.net/clips/Venice_4b_nodither.mp3

Dithered:

http://www.audiochrome.net/clips/Venice_4b_dither.mp3

Noise-shaped:

http://www.audiochrome.net/clips/Venice_4b_noiseshapeE.mp3


And here are solo drums at 5 bit equivalent.

http://www.audiochrome.net/clips/drums_dither.html


There is an entire CD of such signals, published by the AES, that came out of the technical committee I co-chair.

http://www.aes.org/blog/2010/6/digital-audio-educational-cd

As well as some other "interesting" sounds.
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J. D. (jj) Johnston

  • Woodinville
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Dynamic range question
Reply #79
This will probably add confusion to those already having trouble with bits vs dB, but here goes.

It turns out you can get that 96 dB range even with 1 bit samples IF you choose the percentage chance of rounding up (to 1) vs rounding down (to zero) to correspond with the signal voltage.  You do need a lot higher sampling frequency but less component precision and it turns out this is how many/most  DAC's work internally.


This is called "delta-sigma" or "sigma-delta" conversion, both of which are the same thing.  There's a slide deck on how this works at www.aes.org/sections/pnw/ppt/jj/adc.ppt

And PDM (pulse density modulation) or PPM (pulse position modulation) are other ways to accomplish this. Many 'class D' amplifiers use PWM (pulse WIDTH modulation) as well.

All of which use noise shaping to push the noise from the 1 bit quantizer up in frequency to where it doesn't hopefully matter. But SACD has a 6th order Chebychev filter at 50kHz due exactly to that noise causing heartburn for some analog equipment, as it turns out.
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J. D. (jj) Johnston

  • Wombat
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Dynamic range question
Reply #80
There are quite a few studies about TTS (Temporary Threshold Shift). Look for something under that phrase, perhaps.
By the way, I'm not sure how this relates to the aquarium pump, though. If it's low frequncy hum, it won't be masked by high frequencies.
But a bit of low frequency noise will bury it.
Airplanes flying overhead provide a startling amount of low frequency energy. During the post 9-11 flight ban, the silence in our part of New Jersey (USA) was amazing. Then the flights started again, rumble 24/7.

The pump has pretty low frequency hum that is caused by some resonance of the cabinet even when i damped the pump well.
I found several readings about this TTS and really wonder if i already listen to loud when i do my daily listening. Nowhere i found an explanation of how much exatly the treshold is shifted in a way i can relate it to music listening. So playing music with lets say 85dB loudness and how much the ear itself does mask then already. I can imagine that even at this loudness the ear alread canĀ“t hear tones that are only 15db loud when switching off suddenly, or even less when discerning silent elements in the music mix.
I pulled these numbers out of my A** of cause but there must be something to this. If so, the debate about we have to higher higher the dynamic-range of distributed music became even more moot.
Is troll-adiposity coming from feederism?
With 24bit music you can listen to silence much louder!

  • Woodinville
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Dynamic range question
Reply #81
So playing music with lets say 85dB loudness and how much the ear itself does mask then already.


Ok, some basics. Loudness is sensation level. It is not measured in dB SPL.  85dB (I presume you mean SPL) is intensity, not loudness.

85dB average is too loud.  Short peaks are ok to some level above that, but I hesitate to say how much above that.  In order to know "how much the ear masks" you have to know intesity vs. ERB frequency, after dealing with cochlear filttration. Then once you know the loudness, you can estimate the masking spectrum.
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J. D. (jj) Johnston

  • Notat
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Dynamic range question
Reply #82
I'm completely surprised at how good these clips sound...I'd expected there to be nothing left.

We've only removed 3/4ths of the information. We know it's possible to remove much more than that through perceptual coding and still have happy ears.
  • Last Edit: 20 June, 2011, 05:59:17 PM by Notat

  • DonP
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Dynamic range question
Reply #83
This is called "delta-sigma" or "sigma-delta" conversion, both of which are the same thing.  There's a slide deck on how this works at www.aes.org/sections/pnw/ppt/jj/adc.ppt


My department designed a bunch of these in the late 80's for everything from electronic circuit breakers to ultrasound scanners.


  • Woodinville
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Dynamic range question
Reply #84
This is called "delta-sigma" or "sigma-delta" conversion, both of which are the same thing.  There's a slide deck on how this works at www.aes.org/sections/pnw/ppt/jj/adc.ppt


My department designed a bunch of these in the late 80's for everything from electronic circuit breakers to ultrasound scanners.


Hmm, you know Jim Candy, Joe Condon, or Steve Norseworthy? 
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J. D. (jj) Johnston

  • DonP
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Dynamic range question
Reply #85
Hmm, you know Jim Candy, Joe Condon, or Steve Norseworthy? 


Jim Candy sounds familiar, but I was in  sensors and signal processing  at GE Research.

  • Woodinville
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Dynamic range question
Reply #86
Hmm, you know Jim Candy, Joe Condon, or Steve Norseworthy? 


Jim Candy sounds familiar, but I was in  sensors and signal processing  at GE Research.



Ah. I knew the Bell Labs bunch.
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J. D. (jj) Johnston