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BBC Location Recording

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Re: BBC Location Recording

Postby CS70 » Thu Jul 11, 2019 6:39 pm

Hugh Robjohns wrote:Yep. I think my desk calculator has more memory than that today, and my Smart Phone is many orders of magnitude smarter than the navigation computers on the Command and Lunar modules!

So if they could control a spaceship to the moon and back on just 8kB of memory, why the fricking heck does a simple Windows 7 update need 135MB of data? :protest: :lol:

It's all these nice landscape pictures :bouncy:
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Re: BBC Location Recording

Postby hobbyist » Thu Jul 11, 2019 7:49 pm

MOF wrote:
Paul White and I did a double recording of a violin and piano at the Symphony Hall in Birmingham a few years back
One thing I spotted of interest was the lack of hard-drive space to allow 88.2khz sampling, amazing how the cost per megabyte has fallen.
I’m sure if you were doing that recording now you’d be at double that rate and not even considering storage space. I presume classical recordings are done at top PCM rates or DSD these days?


Rate is an interesting question. Some gear will do 96/192/384 and I think I have heard of 768 and even higher although rare.

Theory says that the higher rates are better. Engineering says that A/D sampling accuracy and time clock jitter limit the value of faster rates. And cost will limit how good you would be willing to get better A/D and clocks.

*IF* your A/D and clock stability warranted it then higher rates are the way to go. Storage is dirty cheap now so that is not the constraint we had a couple decades ago.

The downside is that such quality gets expensive. So is it worth it overall to achieve that quality at all? How accurate will your media and playback be? Does anyone consuming your product demand better quality to justify trying to achieve it?

Dont pay no never mind to folks like Lavry who claim that higher rates are not better. He uses logical fallacies in his analysis.
Higher rates may or may not be better depending on your gear.
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Re: BBC Location Recording

Postby hobbyist » Thu Jul 11, 2019 7:52 pm

Hugh Robjohns wrote:Yep. I think my desk calculator has more memory than that today, and my Smart Phone is many orders of magnitude smarter than the navigation computers on the Command and Lunar modules!

So if they could control a spaceship to the moon and back on just 8kB of memory, why the fricking heck does a simple Windows 7 update need 135MB of data? :protest: :lol:

It depends what they are optimising.

Windoze is optimising ease of coding and speed to market.

NASA was minimizing weight and power and was willing to do more programming effort to use a smaller computer.
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Re: BBC Location Recording

Postby James Perrett » Thu Jul 11, 2019 7:52 pm

hobbyist wrote:Dont pay no never mind to folks like Lavry who claim that higher rates are not better. He uses logical fallacies in his analysis.

Would you care to explain these fallacies?
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Re: BBC Location Recording

Postby Hugh Robjohns » Thu Jul 11, 2019 7:58 pm

hobbyist wrote:Theory says that the higher rates are better.

Does it? Better in what way, exactly?

Obviously a higher sample rate gives a wider bandwidth, but how wide is wide enough? ;-)

Engineering says that A/D sampling accuracy and time clock jitter limit the value of faster rates.

Yes, I've heard that too... :lol:

Don't pay no never mind to folks like Lavry who claim that higher rates are not better. He uses logical fallacies in his analysis.

Care to enlighten us?
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Re: BBC Location Recording

Postby CS70 » Thu Jul 11, 2019 9:10 pm

hobbyist wrote:Theory says that the higher rates are better.

No, the theory doesn't. :-)
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Re: BBC Location Recording

Postby hobbyist » Thu Jul 11, 2019 11:13 pm

CS70 wrote:
hobbyist wrote:Theory says that the higher rates are better.

No, the theory doesn't. :-)

Okay -- Theory , with a perfect recovery is perfect.

But there are always errors in real life ; and in real life higher sampling rates could benefit the accuracy of the result IF the A/D errors and clock jitter are small enough.
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Re: BBC Location Recording

Postby Hugh Robjohns » Thu Jul 11, 2019 11:51 pm

hobbyist wrote:...in real life higher sampling rates could benefit the accuracy of the result IF the A/D errors and clock jitter are small enough.

My bovine excreta alarms are sounding here...

Perhaps it would help if you could clarify what you mean by 'accuracy'.

Do you have any credible references for this enhanced sampling theory?

H
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Re: BBC Location Recording

Postby James Perrett » Thu Jul 11, 2019 11:55 pm

hobbyist wrote:But there are always errors in real life ; and in real life higher sampling rates could benefit the accuracy of the result IF the A/D errors and clock jitter are small enough.

As I asked before - can you explain this point a little more? While the need for sample rates slightly higher than 44.1 or 48kHz is well established, I don't quite understand why extremely high sample rates are required for a system where the highest frequency required to be sampled is of the order of 20kHz.
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Re: BBC Location Recording

Postby hobbyist » Fri Jul 12, 2019 12:55 am

James Perrett wrote:
hobbyist wrote:But there are always errors in real life ; and in real life higher sampling rates could benefit the accuracy of the result IF the A/D errors and clock jitter are small enough.

As I asked before - can you explain this point a little more? While the need for sample rates slightly higher than 44.1 or 48kHz is well established, I don't quite understand why extremely high sample rates are required for a system where the highest frequency required to be sampled is of the order of 20kHz.

Because the real physical reconstruction of the analogue signal is not perfect.

There are errors in the timing due to clock jitter, and errors in the amplitude due to A/D/A errors. There is not just a mathematical point that is being used.

This changes what was a nice neat point to a smooshed blob so during the recreation that makes it harder to recreate perfectly.
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Re: BBC Location Recording

Postby Eddy Deegan » Fri Jul 12, 2019 1:09 am

hobbyist wrote:Because the real physical reconstruction of the analogue signal is not perfect.

It doesn't have to be. It only needs to be good enough to accurately capture enough of the waveform such that the reconstructed result is as subjectively good to the listener as the original anlogue signal was.

In the case of human hearing, 44.1Khz is more than sufficient in the vast majority of cases. At this point resolution is more important than frequency and 24-bit is more than enough for the task. Though I may be wrong here my understanding is that 24-bit resolution is effectively 20 to 21-bit due to the noise floor.

For some applications higher rates may be useful, but that's what oversampling is for and as per another recent thread about plugins this is a well understood mechanism which can be catered for within normal digital environments.
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Re: BBC Location Recording

Postby Hugh Robjohns » Fri Jul 12, 2019 9:19 am

hobbyist wrote:Because the real physical reconstruction of the analogue signal is not perfect.

That's true... but then nothing is perfect. The reconstructed analogue signal from a tape recorder or vinyl disc player ain't perfect either. Noise and distortion will always manifest to some degree. The only question is how small do the errors need to be to be inaudible... and we know the answer to that.

There are errors in the timing due to clock jitter, and errors in the amplitude due to A/D/A errors.

Yes... but neither are magically solved by a higher system word-clock rate. Actually both are barely measurable these days, and they are definitely well within the acceptable limits such that they are far below audibility in any conventional application. Quantising amplitude errors were effectively eliminated with the introduction of delta-sigma converters, and system clock jitter was wrestled under control by improved clock generator and clock recovery designs long ago.

Added to which, if the jitter element is random it manifests as a (fractionally) increased HF noise floor, which is hardly going to upset anyone even if they could hear it! If it's not random (but instead related some some periodic function) then the circuit design needs to be reworked.

Either way, though, a higher system word-clock rate means that any inherent clock jitter becomes a significantly higher proportion of the sampling period, and this makes the problem much worse, not much better!

This changes what was a nice neat point to a smooshed blob so during the recreation that makes it harder to recreate perfectly.

Oops... there goes that alarm again... :lol:

H
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Re: BBC Location Recording

Postby CS70 » Fri Jul 12, 2019 9:34 am

hobbyist wrote:
CS70 wrote:
hobbyist wrote:Theory says that the higher rates are better.

No, the theory doesn't. :-)

Okay -- Theory , with a perfect recovery is perfect.

But there are always errors in real life ; and in real life higher sampling rates could benefit the accuracy of the result IF the A/D errors and clock jitter are small enough.

Yes, the math is clear: sampling at double the Nyquist rate maintains all the information in the sampled signal, so the theoretical reconstruction is perfect. There is no information loss. So you don't need anything more.

As of these bothersome engineers, yeah the poor fellows don't seem to be able to mach the beauty and perfection of the math. :D How annoying. But you gotta understand why and what!

For example, increased sample rate require a faster clock! And the faster the clock, the more small inaccuracies in timing become significant. So the higher the sample rate, the more accurate the clocking must be, which as the Romans found out, is quite a lot harder than making a less accurate one. So jitter is a bigger problem at higher sample rates: with the same components and tolerances, you're likely to have a more error in the reconstructed signal, not less - read: worse sound.

As Hugh can explain much better than I, the main issue is that real world lo-pass filtering (which is required to limit the signal to the 20-20K band) is not as perfect as it should be. This in turn may allow some ultrasonic content to alias back in the hearing band. Most mics roll off anyway pretty sharply after 20K, but of course there's some recorded signal that may have content there. 96KHz may help there. Lots of plugins do oversampling for that reason. Tough it helps only if you have ultrasonic content in the first place. I remember he mentioning drum cymbals as a typical source which can benefit (as it's more likely to produce significant ultrasonic energy, which survives the mic roll off attenuation, and may thus get aliased back in the hearing band).

On a practical view tough, I never heard anybody say "hey these cymbals sound odd, probably they've been recorded at 44.1Khz" :-D

Also, keep in mind that 96KHz may put the analogue part of your chain under more strain - and especially with lower end kit, most of the testing has probably been done at the "regular" sample rates. To go over 96Khz for normal musical applications is ... not well thought thru ;-)

Unless it's marketing of course - preying on the honest desire for quality of customers to sell them stuff and even worse, convincing them that the bs is real..
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Re: BBC Location Recording

Postby Ariosto » Fri Jul 12, 2019 9:40 am

So would the experts at SOS recommend 96KHz rather than 44.1KHz (or 48K)? At present I record at 44.1KHz and 24 bit.

I just want to record with the best possible quality and not worry too much about the technicalities, and leave that sort of thing to the really clever people who do such a great job with such brilliant engineering and the data it produces.
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Re: BBC Location Recording

Postby CS70 » Fri Jul 12, 2019 9:43 am

Ariosto wrote:So would the experts at SOS recommend 96KHz rather than 44.1KHz (or 48K)? At present I record at 44.1KHz and 24 bit.

I just want to record with the best possible quality and not worry too much about the technicalities, and leave that sort of thing to the really clever people who do such a great job with such brilliant engineering and the data it produces.

Recording drums or anything with potential ultrasonic content (i.e. over 20Khz) yes. But just record, then you can still downsample in the DAW to 44.1 or 48 to keep file sizes manageable (as if there's an issue, it's the hardware filtering in the A/D converters).

But vocals or guitars, I wouldn't bother. A symphonic orchestra, yes.. That gong there..
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