[sdiy] CD sound quality evolution

Brian Willoughby brianw at audiobanshee.com
Tue Feb 16 07:16:09 CET 2021


Human perception of sound does not work in plain black and white. Frequency response is not flat, sounds at one frequency can mask another; our brains are even so slow that sounds which occur later in time can actually mask sounds that occur earlier in time.

Bit depth is not a cliff where sounds completely disappear below -96 dBFS limit of 16-bit audio. It's way more complex than that. When comparing what's audible to the numbers, there's not a clear line between two distinct opposites.

On the one hand, the human brain can discern sounds well below whatever quantization depth is chosen. This is how 24-bit mastered CD actually sounds better than 16-bit mastering. The 16-bit noise is still all there - it's simply piled into frequency bands that our brains cannot detect quite so well.

On the other hand, the nature of the quantization itself determines whether it is audible. Correlated quantization noise is easily audible, and quite objectionable. Random dither almost disappears - not to test equipment, but to our perception - because we're constantly ignoring Gaussian noise sources in nature to discern quieter sounds that might be important.

AES experts have pointed out that the best audiophile listening setup can achieve only about 18.5 bits of signal to noise. I guess that puts it around 112 dB S/N.

So, yeah, depending upon the kinds of noise that will be picked up even with shielded cables, it is indeed still possible to hear better than 16-bit audio.

You'll never hear all 24 bits, though. The equipment will have more analog noise than quantization noise, although correlated quantization noise will still be audible despite the louder analog noise. Under the best conditions, though, the quantization noise can become inaudible and you're still left with less S/N than the 24-bit DAC handle theoretically produce. This is a blessing in disguise, because all 24-bit DAC chips cannot even hold a steady value due to the massive filter processing going on.

Brian Willoughby


On Feb 15, 2021, at 21:31, Randy Dawson wrote:
> You can't get lower than 16 bits in your home-lab environment with a 1V audio typical signal transport and shielded cables around the room you are working in.
> For 16 bits:
> 2 ^ 16 = 65536
> 1V / 65536 = .00001525878 V (LSB Voltage change)
> 
> I challenge the Golden Ears to toggle this 16 bit LSB above; in their audio chain, from any source in any way, and claim it is audible, or measurable in any audio equipment.
> 
> Randy
> KF7CJW
> rdawson at ieee.org





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