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Analogue versus Digital - Radio 4

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Re: Analogue versus Digital - Radio 4

Postby ef37a » Sun Jun 23, 2019 1:33 pm

Hugh Robjohns wrote:
ef37a wrote:One of the lowest distortion FM demodulators was the pulse counting detector (if done right) Surely that is "digital" with a sampling rate of about 200kHz?

Nope. It's an analogue sampling system. It only becomes digital if the amplitude for each sample is stored or processed as a numeric code... which it's not in a pulse-count detector.

H

Ok, understood.
Elephone: Hugh has mentioned a few times that there are circumstances where 44.1kHz could give problems but I think these are rare and mainly occur with live recording?
I also understand that running at 96kHz removes most if not all of these issues but is not really needed for most of us most of the time?

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Re: Analogue versus Digital - Radio 4

Postby Elephone » Sun Jun 23, 2019 3:06 pm

ef37a wrote:Ok, understood.
Elephone: Hugh has mentioned a few times that there are circumstances where 44.1kHz could give problems but I think these are rare and mainly occur with live recording?
I also understand that running at 96kHz removes most if not all of these issues but is not really needed for most of us most of the time?

Dave.

Thanks. The video I linked to specified a problem with analogue simulation plugins. I presume they add harmonics or reinforce them via saturation and these cannot be managed when they spill over the 44.1kHz threshold without spilling back into the audible frequency range from 22.05kHz unless oversampling is used.

The video suggests this problem doesn't occur with his real analogue mixing desk, but only because it passes through the audio interface and gets attenuated as it passes through the filter at the A-D converters. It is suggested that the problem lies with plugins that don't offer oversampling.

I read that a lot of plugins, especially analogue emulations don't respond well when fed cranked up levels, and people assume you need crank everything up, that this is why analogue emulations might not produce as good results as people want or expect.
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Re: Analogue versus Digital - Radio 4

Postby Hugh Robjohns » Sun Jun 23, 2019 9:12 pm

We discussed this issue in another thread:

https://www.soundonsound.com/forum/viewtopic.phpf=22&t=66679&hilit=Robjohns%20+oversampling#p608652

Where complex non-linear processing is involved there will be a lot of strong harmonics, and working at a higher sample rate makes the calculations easier, hence the oversampling, while the anti-alias filtering used when down sampling cleans the spectrum up properly.

H
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Re: Analogue versus Digital - Radio 4

Postby N i g e l » Tue Jun 25, 2019 3:46 pm

Just caught up with this, listening to the podcast on my portable audio player.

I like digital. For me, digital is democratising, more convenient, less maintenance and gives me quality and functionality at a nice price.

The mathematics of sampling and reconstruction from the 1930’s is spot on but the engineering of circuits and techniques to implement the mathematics is still evolving, as the limiting factors of the circuit techniques, psycho accoustic effects and the things they didn’t think of are all understood and corrected to give better audio quality for less money.

The original “CD quality” must be getting on for 40 years old now ?

I was recently surprised to hear of a design improvement to 1-bit DACs to reduce audible artifacts that manifested below the noise floor at over 100kHz !

But Digital v Analogue is much bigger than different sets of noise and distortion figures. There are consequences, social and musical !

Digital has put people out of work, changed work flows, closed factories, closed studios, allowed archival copying of disintegrating master tapes from the 1950’s, allowed copying of chart music from last week, impacted profit margins ...........

I have been greatly inspired by the music of the BBC Radiophonic workshop and their creative use of tape and tape recorders.

A composition that took them a week to record, slice and edit, I could probably now recreate in a morning using my sampling & multitrack software with non linear editing.

As a home musician that’s all very nice for me but for professionals, it means that a process which may have involved 10 tea breaks, 5 lunches and 4 good nights of sleep is now reduced to having only has a single break (perhaps you could skip tea break & work straight thru to lunchtime to guarantee the deadline...? )

“Sometimes its the spaces between the notes that make the music”
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Re: Analogue versus Digital - Radio 4

Postby Elephone » Tue Jun 25, 2019 4:42 pm


Thanks. That link didn't work but I corrected it in case anyone wanted it:

https://www.soundonsound.com/forum/view ... 9&start=40
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Re: Analogue versus Digital - Radio 4

Postby Arpangel » Wed Jun 26, 2019 8:11 am

N i g e l wrote:The original “CD quality” must be getting on for 40 years old now ?

Yes, and I've been happy with it from day one, and I always record in 44/16. It's always fine for what I do. I've tried higher bit rates, but I cant hear any difference.
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Re: Analogue versus Digital - Radio 4

Postby blinddrew » Wed Jun 26, 2019 8:28 am

Well, 16bit gives enough dynamic range for any practical purposes so unless something goes wrong you shouldn't hear any difference.
Recording at 24bit just gives loads more dynamic range so you can drop your levels and give yourself loads of headroom when recording.
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Re: Analogue versus Digital - Radio 4

Postby ef37a » Wed Jun 26, 2019 9:31 am

blinddrew wrote:Well, 16bit gives enough dynamic range for any practical purposes so unless something goes wrong you shouldn't hear any difference.
Recording at 24bit just gives loads more dynamic range so you can drop your levels and give yourself loads of headroom when recording.

I always say "twenty four bits gives you more LEGroom"!

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Re: Analogue versus Digital - Radio 4

Postby N i g e l » Wed Jun 26, 2019 12:49 pm

16 bit is ok for CD playback as the audio will have been optimised to fit.
For recording on the PC, I find it easier to set the levels with 24 bits, as Blinddrew says, more headroom to avoid clipping.

Is a CD track today the same as it would have been in the 80’s or can they now do additional processing purely to the digital data (eg dithering or better dithering) to make it sound better on the playback machine ?

I use 96kHz to record on the PC ostensibly because a have a synth and some VSTs that run at 96k but mainly because I have that option on my sound card so I might as well use it. With modern hard disk sizes the extra data isn’t a burden to me. Theres a good SOS article on 96k and alising somewhere.

I also have a “studio in a box” hard disk recorder for PC-free jamming / practice (can be very good value on Ebay these days). Its 44.1k/16 bit and does a very good job.

I think It is worthwhile recording at the best quality you can as you never know what innovations and quality improvements future gear will have that show up flaws in recordings made today.
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Re: Analogue versus Digital - Radio 4

Postby The Elf » Wed Jun 26, 2019 1:22 pm

The extra head/leg-room of 24-bit is very useful and the cost is minimal by modern standards. I can't see much value in tracking at 16-bit.
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Re: Analogue versus Digital - Radio 4

Postby N i g e l » Wed Jun 26, 2019 1:42 pm

In quality terms, how far did top flight analogue tape equipment get ?

Had it reach a plateau, or if Digital hadnt come along, would it have evolved further?
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Re: Analogue versus Digital - Radio 4

Postby MOF » Wed Jun 26, 2019 2:26 pm

In quality terms, how far did top flight analogue tape equipment get ?

Had it reach a plateau, or if Digital hadnt come along, would it have evolved further?

Off the top of my head I seem to remember that analogue tape had a maximum of 60dB dynamic range. Dolby SR was very effective in noise removal without any obvious artefacts.
Running at 30 ips might have improved on those figures for improving frequency response and dynamic range (albeit with a reduced bass response) and changing the head block from 24 tracks on 2” tape to 16 tracks improved dynamics and bass response but that doubled your cost and you lost eight tracks, if you synchronised two machines you lost a further two tracks to timecode and four if you left a safety track to stop timecode bleeding into the audio tracks, and of course you needed two machines and a synchroniser.
I think the technology had plateaued, much like film versus digital cinematography, and the speed of operation and storage space/cost required, the ability to make perfect backups, the absence of noise, tape’s self erasure at high frequencies etc etc make digital the way to go.
If analogue tape and silver nitrate film had just been invented and you already had the digital versions, no one would be interested.
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Re: Analogue versus Digital - Radio 4

Postby Hugh Robjohns » Wed Jun 26, 2019 3:03 pm

N i g e l wrote:16 bit is ok for CD playback as the audio will have been optimised to fit.

Very little recorded audio has a dynamic range anywhere near 90dB, so it's not a case of 'being optimised to fit' -- 99% of all recorded audio would fit comfortably anyway.

But 16-bit is more than sufficient for CD (or any domestic format) as some simple sums quickly reveal. The typical ambient or background noise of a quiet lounge, say, in a quiet suburb in the dead of night, is going to be around 30dBA. More likely it's closer to 40dBA... (A professionally designed and constructed studio control room will often have a background noise level of 25dBA, and some can be down to 15dBA across the mid band frequencies -- but that's getting very specialised, very difficult, and very expensive).

So, if the domestic listener adjusts the volume of his mega-expensive super-dooper hi-fi to set the dither noise floor of the CD at or just below the ambient room noise, then full scale digital peaks will be around 93dB higher... which is at least 123dBA, and potentially over 130dBA. Not only is that painfully if not damagingly loud, it would be one heck of a good hi-fi that could actually generate that kind of sound pressure level (for more than one snare hit!).

Therefore there is zero benefit in using more than 16-bits for any consumer release format. The extra dynamic range capability would be wasted even if material could be found that made genuine use of it, and the reduced noise floor would be inaudible anyway below the ambient acoustic noise floor.

However, for source recording there are very sane arguments for using 24 bits to allow additional headroom to cope with unexpectedly loud transients peaks etc, and for post-production even greater dynamic range can be helpful, which is why the 32-bit fixed or float formats are generally employed (and now 64-bit float in some systems -- but more for convenient programming than any real sound benefit)

Is a CD track today the same as it would have been in the 80’s or can they now do additional processing purely to the digital data (eg dithering or better dithering) to make it sound better on the playback machine ?

Actually, some of those early 80s CDs didn't have any dithering at all (and you're careful you can sometimes hear the reverb tails and track noise breakup in the quietest end of the fade-outs as a result!). I think it's true to say that A-D performance, in particular, has improved quite significantly since the first generation of CD mastering recorders, and the introduction of psycho-acoustic noise-shaped dither systems has also been beneficial. D-A conversion has also improved with oversampling and delta-sigma techniques, as have the all-important clocking technologies, of course.

So no, a modern CD track wouldn't be the same, it would be better... except that in the 80s the loudness war hadn't really got going, so although material was being peak normalised in mastering, it wasn't being limited and compressed until the pips squeaked, which is largely is today... So while the technical sound quality today is better than the 80s, the musical quality is, IMHO, often significantly lower.

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Re: Analogue versus Digital - Radio 4

Postby Hugh Robjohns » Wed Jun 26, 2019 3:18 pm

N i g e l wrote:In quality terms, how far did top flight analogue tape equipment get ?

Had it reach a plateau, or if Digital hadnt come along, would it have evolved further?

No, it probably wouldn't and couldn't have been developed any further. The technology was about as good as it was possible to make it -- both in terms of the machine's mechanics and associated electronic control systems, and in the audio electronics and associated signal processing (like Dolby SR and Dolby HX). and also in the tape formulations. All of these areas had been evolving over 50 years and there was just no engineering avenue or technology left to exploit.

Importantly, though, achieving that ultimate level of quality was extremely expensive and difficult. A high-end two-track tape machine cost upwards of £12k-£15k, and then there was the material cost of tape to record on it which wasn't cheap either, and these machines needed constant alignment and maintenance, often involving expensive replacement mechanical parts -- which required skilled (expensive) studio engineers.

When digital studio recording audio became a practical reality in the late 80s and early 90s it did so with equal or better tech specs and at a fraction of the cost -- initially a mastering grade PCM1610 digital encoder and U-matic machine cost around two thirds as much as a high-end mastering two-track tape machine, and by the time studio-grade DAT machines appeared the cost was down to less than a third... and the costs continued to fall from there.

And then the desktop computer became affordable and commonplace, and digital audio moved from bespoke and dedicated audio machines onto general purpose computers... and the prices tumbled even further and capabilities went through the roof...

So, whatever the validity of the 'analogue sounded better' arguments -- and I agree that it did in the early days -- it was the cost and convenience of the digital revolution that killed the mainstream use of analogue tape, and hence digital quickly took over in every area.

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Re: Analogue versus Digital - Radio 4

Postby N i g e l » Wed Jun 26, 2019 11:01 pm

Thanks ! thats an interesting bit of history.
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Re: Analogue versus Digital - Radio 4

Postby CS70 » Thu Jun 27, 2019 12:15 am

N i g e l wrote:A composition that took them a week to record, slice and edit, I could probably now recreate in a morning using my sampling & multitrack software with non linear editing.

As a home musician that’s all very nice for me but for professionals, it means that a process which may have involved 10 tea breaks, 5 lunches and 4 good nights of sleep is now reduced to having only has a single break (perhaps you could skip tea break & work straight thru to lunchtime to guarantee the deadline...? )

“Sometimes its the spaces between the notes that make the music”

Yeah a very good consideration. The actual issue with digital machines is that they revolutionize every field they are deployed to, with all the consequences that a revolution brings - even a benign one.. Audio is just one of the many fields, and all considered, among the less relevant.

There's plenty fields where still to deploy digital technology. The next centuries are gonna be mightly interesting.
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Re: Analogue versus Digital - Radio 4

Postby Arpangel » Thu Jun 27, 2019 8:16 am

The dynamic range of an orchestra is about 80db, 16 bit is 120 I think, anaolgue recording tape is much less than either of these, about 60db maybe.
High bit rates are a bit like.....well, it's there so let's use it.
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Re: Analogue versus Digital - Radio 4

Postby Hugh Robjohns » Thu Jun 27, 2019 9:42 am

Arpangel wrote:The dynamic range of an orchestra is about 80db

Yes, pretty much -- if the musical work is written to use it and the orchestra capable of playing it, and the hall's ambient noise floor quiet enough. For someone sitting in the ideal auditorium seat, the peaks will be to around 100-110dBA, and the quietest musical ppps around 20-30dBA (plus the obligatory coughing).

Image

...16 bit is 120 I think

The theoretical signal-noise ratio of a 16 bit digital system is about 96dB, but that's when undithered which isn't a lot of use... so with dither you're looking at about 93dB -- but the benefit of dither is that you can then hear undistorted quiet sounds below the noise floor which potentially adds 10-20dB to the audible dynamic range capability.

So assuming the gain structure is set carefully, 16-bit can cope with the full range of an orchestra without any difficulty.

...anaolgue recording tape is much less than either of these, about 60db maybe.

The signal-noise ration of raw analogue tape is about 60dB (depending on tape/track width and speed). Dolby A added roughly another 10dB or so to that (mostly at the intrusive high frequency end), and Dolby SR pushed that up to around 25dB -- so potentially an 80-85dB signal-noise ratio.

Again, you can hear quiet sounds below the theoretical noise floor of analogue tape, buried in the hiss but still audible. The biggest practical difference, though, is that loud sounds on tape are progressively distorted, whereas they aren't in a digital system.

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Re: Analogue versus Digital - Radio 4

Postby The Elf » Thu Jun 27, 2019 9:54 am

Arpangel wrote:High bit rates are a bit like.....well, it's there so let's use it.
Bit rates and word lengths are significantly different subjects.
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Re: Analogue versus Digital - Radio 4

Postby CS70 » Thu Jun 27, 2019 9:58 am

Hugh Robjohns wrote:Yes, pretty much ....

Very cool graph, Hugh!
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