John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
So, really a digital system needs to be 10x better resolution than 16 bit to have a hope of matching the distortion characteristics of analog at -18dB average levels.
Maybe somebody can do the maths, but on simple reckoning that means 21 bits real resolution is required for digital systems to compare to analog in the real world..
Sorry, Dan, I can't go along with this - theoretically, and practically, 16 bits are fine. I've done various types of fiddling over the years, in experiments of reducing number of effective bits used for encoding, and application of dithering - and it all works like it's supposed to. If you're hearing distortion artifacts in some situation then it's because the implementation is faulty, or the design of the decoding mechanism is flawed. Apart from the single, badly mastered opera recording I've mentioned a couple of times, I haven't heard bad sound because of digital format "deficiencies" intruding.
 
Last edited:
Dan, unless one does something silly with the (analogue) gain control the distortion harmonics are always going to be buried in the listening room background noise - the signal level may drop, but the distortion levels stay constant, with respect to that background noise ... you just won't be able to hear any artifacts.
 
Sorry, Dan, I can't go along with this - theoretically, and practically, 16 bits are fine. I've done various types of fiddling over the years, in experiments of reducing number of effective bits used for encoding, and application of dithering - and it all works like it's supposed to. If you're hearing distortion artifacts in some situation then it's because the implementation is faulty, or the design of the decoding mechanism is flawed. Apart from the single, badly mastered opera recording I've mentioned a couple of times, I haven't hear bad sound because of digital format "deficiencies" intruding.
Somebody here (RNM ?) stated that the Philips engineers responsible for CD standard opined that 16 bit was not actually good enough.
Of course technology and market forces determined the Red Book standard.
I do agree that 16 bit on a correctly sounding system sounds quite fine.

However......

A few months back I repaired a vinyl system for a friend and played a mint Helen Reddy vinyl that I had on hand, and also digital copy that I am well familiar with.
I had run up the system on a selection of usb digital and CD before he came to collect and all sounded good.
When he arrived I played the HR vinyl and I was floored compared to the digital version.
So much more presence/articulation/clarity that I had not heard in a long time due to my digital only PB for yonks.
I have a Dual 505 and selection of cartridges in the garage...when I get a roundtuit I will try some more listening comparisons to refresh/confirm my memories of what vinyl can really do.

The digital PB system that I have running currently is quite stunningly good, that said I am playing mostly pop/rock/jazz which by definition run at elevated average levels, and do not really reveal really low level non linearities in DAC output stages as to be expected when running orchestral music.

Dan.
 
Dan, unless one does something silly with the (analogue) gain control the distortion harmonics are always going to be buried in the listening room background noise - the signal level may drop, but the distortion levels stay constant, with respect to that background noise ... you just won't be able to hear any artifacts.
My listening room is well damped and essentially silent....come 7:00/8:00 pm there are no traffic/suburban/neighbour noises/sounds to interfere.....seriously.

Dan.
 
Last edited:
Last night, my wife (who was not in the kitchen) and I watched a delightfully goofy demonstration on Penn & Teller's TV series, the name of which is automatically censored by the forum software. It had nothing to do with audio, it was about organic food. They set up a booth at a farmers' market and had a side by side blind comparison of so-called organic versus non-organic produce.

Scroll to 2:45.

https://www.youtube.com/watch?v=8Zqe4ZV9LDs

Language warning for the sensitive- they talk pretty much the way I do. The adjectives are amazingly familiar, as are the excuses. :D

"Which of these feels better to eat" :rolleyes: Many folks preference for organic has nothing to do with taste.
 
I'm sure you do, as well as most everyone in this thread. But you REALLY need to watch the demo at 11:45. It will make your blood boil.

He was past president of the AES and still sits on a number of committees. I wonder if the AES would approve?

se

Stunning, I guess he doesn't believe in standards. BTW I hope Richard realizes eventually that the total THD + noise is always > the single highest peak spurious tone. His current definition of DNR is far more lenient than (dare I say) the standard one.
 
Between home PC and lunchtime smart phone I might have missed you link.
Please refresh me.

Thanks, Dan.

Dan, I suggested a simple experiment. Mathematically generate an arbitrarily complex waveform (like a multi-tone) at 64bit precision and truncate and dither it down to say 24 bits. Then subtract the original, the residue is indistinguishable from random noise. There is no systematic error on any time scale, but you have lost 3dB SNR. Folks show typical sine wave FFT demos but the principle works for any waveform. Dither far predates digital audio and has a sound mathematical background.
 

Attachments

  • dither.pdf
    76.7 KB · Views: 50
Last edited:
Ok, thanks for that Scott.
I should do the experiments you suggest, and also repeat my previous experiments.

The pdf you quote gives levels of quantisation noise lower than -100dB, with differing spectral nature according to the dithering type.
What is interesting is that these different ditherings are noted as sounding different and ranked according to perceived loudness.
This paper reinforces my previous statements about differences in audibility of differing dither types (Mash, Sony, Cool Edit etc).
The fact that eons ago I picked up on these to me audible differences prior to my in depth knowledge of dithering theory reinforces the fact of audibility of -100dB noise/distortions.
IMHO this info actually reinforces the notion that better than 16 bit systems are required.

Dan.
 
Ok, thanks for that Scott.
I should do the experiments you suggest, and also repeat my previous experiments.

The pdf you quote gives levels of quantisation noise lower than -100dB, with differing spectral nature according to the dithering type.
What is interesting is that these different ditherings are noted as sounding different and ranked according to perceived loudness.
This paper reinforces my previous statements about differences in audibility of differing dither types (Mash, Sony, Cool Edit etc).
The fact that eons ago I picked up on these to me audible differences prior to my in depth knowledge of dithering theory reinforces the fact of audibility of -100dB noise/distortions.
IMHO this info actually reinforces the notion that better than 16 bit systems are required.

Dan.

I hope you didn't miss this... "After quantization, the noise samples were amplified
by 40 dB for easy listening."
 
Disabled Account
Joined 2012
View attachment 467678
Richard's point here is perfectly valid..ie 16 bits rec/pb system incurs significant distortions at mid levels which is where 'correctly' recorded orchestral, jazz, old school pop/rock etc music inhabits most of the time.
By 'correctly', I mean levels that comply with the old standards..ie -18dBFS average level which generally leaves sufficient peaks headroom for the above mentioned music genres. (much modern music is highly compressed/peak limited even when played live in studio so may not conform to/require the 18dB+ headroom spec historically used).

So, when playing back 'correctly' recorded programme on 16 bit systems, the playback DA convertor stage is indeed running at average levels way below (10% of) the maximum output levels that measure close to perfect and arguably inaudible.
So, straight away 20dB of noise and distortion 'perfection' is 'thrown away' in order to capture peak level without incurring distortion.

Tape systems and vinyl systems do not 'fall apart' when running at -20dB average level in the manner that 16 bit digital does.
Digital becomes more distorted as level decreases, analog systems do not become more distorted as level decreases, but do suffer masking due to intrinsic wideband noise.
That said the nature of analog system wideband noise is generally white/pink in nature, and is easily discounted or 'listened through' by the ear.

So, really a digital system needs to be 10x better resolution than 16 bit to have a hope of matching the distortion characteristics of analog at -18dB average levels.
Maybe somebody can do the maths, but on simple reckoning that means 21 bits real resolution is required for digital systems to compare to analog in the real world.

Never mind that 24 bits real resolution is pretty much unattainable in real world consumer PB systems, but 21 bits real resolution is probably what is generally attained in current 24 bit claimed consumer systems.

In order for digital systems to compete with analog/vinyl systems, music distribution does indeed need to be at least 24 bit for the typical consumer to correctly hear music as it was intended.

Sampling rate is another issue, but at least one of the benefits of higher Fs is slower/lower DAC output filtering roll off slope.
This lower slope/phase change does provide sonically beneficial results.
With any digital system, the amplification chain must have HF capability to ensure lack of LSB production.
LSB production is one factor that ruins sound on many systems.

Dan.


You got the point, clearly and cleanly.

:cool::)



THx-RNMarsh
 
Status
Not open for further replies.