Topic: 20 bit converter, 16 bit DAT..where does the 4 extra bits go?

[phishn]

How is it decided what 4 bits to drop?

[cpclark]

im sure all 20bit boxes have an algorithm that they use to decide what to take out and what stays

[gonads]

converters use an algorithim designed to "dither" down the 18(ad500e), 20, or even 24bit data which the a/d converter puts out to 16bits for the dat deck. Some popular dithering algorithms are Apogee's uv222 and Grace's ANSR.

If you do not utilize ANSR or UV222 or some other algorithim you will be "truncating" the extra bits. "Truncating" results in the extra bits being cast aside instead of rounded off and can result in some unpleasant sounding digital artifacts.

This is just a very brief overview, there's lots of info on all of this at the library or on the internet but now you know what to look for.

Here's a decent link with some audio samples

http://www.mtsu.edu/~dsmitche/rim420/reading/rim420_Dither.html

[Sean Gallemore]

dither rox!

[cpclark]

converters use an algorithim designed to "dither" down the 18(ad500e), 20, or even 24bit data which the a/d converter puts out to 16bits for the dat deck. Some popular dithering algorithms are Apogee's uv222 and Grace's ANSR.

If you do not utilize ANSR or UV222 or some other algorithim you will be "truncating" the extra bits. "Truncating" results in the extra bits being cast aside instead of rounded off and can result in some unpleasant sounding digital artifacts.

This is just a very brief overview, there's lots of info on all of this at the library or on the internet but now you know what to look for.

Here's a decent link with some audio samples

http://www.mtsu.edu/~dsmitche/rim420/reading/rim420_Dither.html

thanks for the more explicit description of dither gonads, +T

[gonads]

it's complicated and involves math (yuck!) but the basics aren't too complicated.

[phishn]

thanks for the explanation.

[Cooker]

i believe the graham-patten boxes truncate the 20 bit signal, while the sbm-1 dithers a 20-bit signal.

[gonads]

that would explain a lot about the gp boxes.

and yes, sbm stands for super bit mapping.. it is sony's algorithim ala Apogee's uv222 and Grace's ANSR

[cpclark]

it's complicated and involves math (yuck!) but the basics aren't too complicated.

I saw a math formula the other day in the M-S thread, open forum



here it is;
The M/S matrix takes the sum information M + S, and sends it to the left channel, and the difference information M - S, and sends it to the right channel. When the left and right signals are combined, (M + S) + (M - S) = 2M, the sum is M information only. :sonar: :propeller:

mike-this is a simple algorithm used to decode the mid-side techniqe for mics  not a dither from 20->16 bits, the dither algorithms are and im pretty sure, very complicated math

[DaryanLenz]

While we are on the subject...apogee's uv22hr is pretty standard, but I was wondering which people prefer sound-wise?

Daryan

[cpclark]

I realize its not an algorithim. Its math!

Thank the almighty I'm an artist, because I suck at math!

same here, math not as good as it used to be

[MattD]

In English, the job of the dither algorithm (when dithering to 16 bit, in this example) is to take the 15 most significant bits from each sample and use noise as the 16th bit to mask the quantization noise. I *think* this noise is what largely differs from one algorithm to the next. Some use certain frequencies of noise (noise shaping), others use pseudo-random noise, and at least one uses analog random noise.

Quantization (to 16 bits in this case) inherently creates some noise and the use of the last bit is a means of making this noise inaudible in one way or another - by pushing it past the limits of human hearing, by making it random and thus not 'picked up' by our brains, or some other means.

Perhaps those more versed in psychoacoustics or FFT-based math can explain this better than I just tried to.

-Matt