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  #121  
Old 02-05-2002, 10:43 AM
Doug Ring Doug Ring is offline
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Default Re: Protools 192k

Okay Nika, back in your knife-box, Mr Sharp [img]images/icons/smile.gif[/img]

I get your drift now: 192 is a different way of doing things and need not inherently sound better than 44 from the same manufacturer. But it's not as though Digidesign are first into the swimming pool with 192 - I've read many reports of other people using it and claiming differences in the sound. I think the SADiE system has done 192 for a while, as has the four-track digital Nagra, the latter having been used by one of the writers in Stereophile magazine. So there's a growing body of evidence that something is going on with high-sampling-rate systems. To put it another way, how many manufacturers' razor sharp ceramic knives would you have to use to think there was a worthwhile difference and that ceramic might be the way forward for knives?

I confess I've not heard any high-res systems myself, apart from an early trial with 100kHz sampling on a Synclavier. From memory, the difference was there, but it wasn't sufficient to merit gobbling up more than double the storage space. After all, 10 years ago we only had 8 track-hours at 44, and that was on a £250,000 system! Don't get me wrong, as long as 44 sounds good enough, I've no wish to quarter my own available storage by going to 192 these days either, but I'm interested to see what will become of it and whether there'll still be people clinging to the 44 raft in ten years time.

BTW, earlier you stated that we can't hear whether a 15kHz signal is a sine or a square wave because we can't hear even the first harmonic necessary to turn a 15k sine wave into a square. This may be true, but I don't think it's relevant to how we actually hear. We don't analyse combinations of waves as if we had an oscilloscope in our head. From my hazy recollections of university lectures, hearing, like vision, is not a purely passive process and involves quite a lot of cognitive effort. It may be that we can respond to the rise-time of a wave even though we can't hear all of its components. That, I think, is one reason why we can usually tell a live instrument from a recorded one.

After your assertion, I put the Audiosuite Signal Generator plug-in on to a track and set a sine wave to ...well, 14.8kHz {my 1954 birthday means I can't hear 15k [img]images/icons/frown.gif[/img] ...). Things became interesting when I switched to square, however. I could hear THAT alright! A whole series of beat notes appeared, and if you swept the frequency around, all the beat notes swept with it, like tuning a short wave radio. If you want to scare yourself about the quality of Digi's converters, don't try this at home! (I did, actually, and it does it on an 001 as well as a TDM). I think there's something other than distortion going on here; anybody like to hazard a guess what?
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  #122  
Old 02-05-2002, 11:12 AM
Chris Townsend Chris Townsend is offline
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Default Re: Protools 192k

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Doug Ring:

Things became interesting when I switched to square, however. I could hear THAT alright! A whole series of beat notes appeared, and if you swept the frequency around, all the beat notes swept with it, like tuning a short wave radio. If you want to scare yourself about the quality of Digi's converters, don't try this at home! (I did, actually, and it does it on an 001 as well as a TDM). I think there's something other than distortion going on here; anybody like to hazard a guess what?
<HR></BLOCKQUOTE>

The distortion you are hearing is not a factor of the converters. It will sound essentially the same whether you are using Apogee, Digi, or any other converter. What is actually happening is the upper harmonics of the square wave are aliasing (folding over) causing a distorted sound. This can be improved, but at the expense of CPU usage.
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  #123  
Old 02-05-2002, 11:21 AM
Chris Townsend Chris Townsend is offline
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Default Re: Protools 192k

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by emilano:
McGriffy,

Fine, if what you're saying is true, then why don't the manufacturers just make a better 44.1khz convertor? Why make them high sample rate systems that have to deal with a bunch of possibly useless extra info that makes us use up all our DSP and give us less tracks to work with.
<HR></BLOCKQUOTE>

One constraint on converters is latency. If, for example, you want to keep the latency below 2 ms then that puts unavoidable contraints on ripple, stop band rejection, etc. If latency (and calculation power) is not a constraint, then these factors can be made as good as you like, but at 96k you can have much lower latency and much better filter response simultaneously.
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  #124  
Old 02-05-2002, 03:38 PM
Doug Ring Doug Ring is offline
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Default Re: Protools 192k

Thanks for the reply, Chris. I realise that a 15k square wave is not a "real-world" signal, but it's still a little scary to see this amount of aliasing happening at 44.1kHz sampling. Some real-world signals must be doing this to the convertors - a piano for example. This might explain why it's so hard to record that instrument realistically. It would seem, then, that 192 will push the window before aliasing further up the frequency spectrum and may contribute to a sweeter top-end.

Any comments on that, guys?
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  #125  
Old 02-05-2002, 05:37 PM
tech_head tech_head is offline
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Default Re: Protools 192k

Hi,

An example Crystal Semi A/D takes a
1024x clock at 48Khz. This means the sample
frequency is ~50Mhz. This also means that
the stop band filter can be a real simple active circuit with 6db/octave roll-off
above 300Khz.

By the time you get anywhere near the
actual sampling frequency there is no
energy left at all.

The actual anti-aliasing filter is a digital
filter with ideal phase response in the
pass band which is 48Khz.

There is no recorded aliasing in the real world.

There is a lot of speculation around here about sound of converters, sample rate,
blah, blah, blah, blah.

You could never record a true square wave
on any bandwidth limited medium so the
experiemnt you did was flawed.

What you heard was the D/A converter trying to respond to an out of band signal and
doing a horrible job of it.

tech
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  #126  
Old 02-05-2002, 08:11 PM
D Clementson D Clementson is offline
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Default Re: Protools 192k

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by tech_head:
Hi,

An example Crystal Semi A/D takes a
1024x clock at 48Khz. This means the sample
frequency is ~50Mhz. This also means that
the stop band filter can be a real simple active circuit with 6db/octave roll-off
above 300Khz.

tech
<HR></BLOCKQUOTE>

tech_head:

You are misinformed about that sampling rate. All Crystal ADCs sample at 3.072 MHz. AKM too. There is an internal prescaler on the MCLK pin. That info is direct from the chip designers. You're right about the simple anti-alias filter, though.

DC
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  #127  
Old 02-05-2002, 11:16 PM
john1192 john1192 is offline
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Default Re: Protools 192k

i would like to say something...who are we to believe...i read tech info from people and then i read tech info from other people on this forum...i can be very confused...Digi say the tech's are wrong and the tech's say Digi is wrong...i am going to one of the other forums, as i do not trust anything i read here anymore...you all sound like you know what you are talking about...where is the truth...it is not about money it is about making music and learning the truth about how to record digital music and sound...please lets come to a conclusion...if you do not know the answer or are unsure, please do not post your opinion...including Digi...if i take someone for there word and do not look back four minutes later to see that there is a completely different conclusion then who is at the loss.....me.....i am going somewhere else....you are all scaring me...all i want is the truth...and the knowledge to do my job the best i can....happy hunting for all that search for the truth...john
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  #128  
Old 02-05-2002, 11:58 PM
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Default Re: Protools 192k

That seems kind of silly. The posts in this topic are from the Digidesign engineers that designed and built the hardware and software being discussed. They're not marketing or sales people, and have presented an enormous amount of factual information. There's a great deal of technical detail that I don't personally understand either, but I don't doubt the veracity of the Digi engineering statements one bit. If you don't want to believe them, that's your choice, but I can't imagine where you would get more accurate information. But by all means, go forth and seek. [img]images/icons/smile.gif[/img]
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  #129  
Old 02-06-2002, 05:03 AM
Nika Nika is offline
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Default Re: Protools 192k

Wow...

It seems to me that we're agreeing most of the time. At least that's the sensation I've had. I'm sorry you don't seem to be experiencing that.

Nika.
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  #130  
Old 02-06-2002, 09:02 AM
john1192 john1192 is offline
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Default Re: Protools 192k

i my self am fully inclined to believe you, Digi, when it comes to your products who would know them better. i am asking then Tech Head, do you believe you are correct or do you agree with Digi on their statement....just a silly question from a mixer that is not a bench tech...of which i have many friends that are my most admired friends...you build the things we drive...i am just looking for the end of the line, if there is one............maybe there really is no spoon.....
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