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Author Topic: 88.2 & 96k playback problem  (Read 4499 times)

Ed Littman

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Re: 88.2 & 96k playback problem
« Reply #15 on: July 30, 2005, 09:59:20 am »

yes, it's working with the format converter.
Just curious at this point...

I did think that spdif can can run over a aes/ebu cable with no problems.....humm

My aes/ebu cable length is about 25 ft.

no faulty cards, the same issue happend on a third rme card in another computer.

using the clock from my adc or internal respectfully gets the same result.

no problems when it's spif all the way.

thanks for the input,
Ed
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Chris Cavell

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Re: 88.2 & 96k playback problem
« Reply #16 on: July 30, 2005, 10:06:45 am »

The change in clocking frequency can have an impact on the load requirements (which you need to meet to prevent transmission line reflections).  The change is usually in how strictly you have to adhere to the requirement, and less often a change in value. There are too many factors that come into play to say why one person's setup actually works in this situation...but suffice it to say that the effects of reflections on a working setup are small enough that they don't have an impact large enough to completely lose sync (you might however be encountering an undue amount of jitter and simply not realize it).

Everything from a tiny cold spot in a solder joint to a minimal amount of oxidation at the connection can have pretty drastic influences on the reflective property of the connection.  It may be that Ed's setup is encountering these very difficult to narrow down elements, or that his system is simply more sensitive to transmission line reflections.

I found a little animated GIF that shows the effect reflections can have on your clocking...kind of anyway, but picture instead of a single pulse (as in the GIF) what can happen as additional pulses are sent WHILE the reflections are bouncing around:
http://courses.ncsu.edu:8020/ece480/common/htdocs/images/aa- xmission-trm.gif

Cheers,
Chris
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Ronny

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Re: 88.2 & 96k playback problem
« Reply #17 on: July 31, 2005, 04:14:59 pm »

bblackwood wrote on Sat, 30 July 2005 08:21

Ronny wrote on Sat, 30 July 2005 07:04

Higher fs does not mean that the signal travels twice as fast as the halved sample rate, only that it's being sampled twice "as much", all frequencies travel at the same rate, although not the same energy. If freq's traveled at different speeds all your ears would hear would be beat frequencies and harmonic structure would be nigh impossilbe to capture and reproduce. I guess we'll just have to disagree on this one, Brad.

No, you simply don't understand what I'm saying.

It's a fact that higher fs means that data is crossing the zero point at a faster rate in any given period of time. That's what sampling frequency means, Ronny - that in one second period of time, you have 96k sampled versus 44.1k samples. The greater number of samples means that you have more instances of zero crossings in any given time period - hence the term 'faster'.

No one is suggesting that the actual signal travels faster through the wire, but higher sampling frequencies means that the signal appears 'faster' to the receiver chip (not faster from point to point, but the number of zero crossings/given time period), and the impedance can definitely have an impact on higher freqs...




The frequency determines the zero crossing, it doesn't matter what sample rate that you sample a frequency at, provided that you follow Nyquist and have enough samples per second to include the the whole wavelenghth. Below are two pictures of a 10k tone at -6dB one sampled at 44.1k and the other sampled at 96k. I chose a 10k tone because one complete wavelength both positive and negative sides of the frequency is 100 samples when sampled at 44.1k. As you can see there is still only one zero crossing at either sampling rate. The timeline has not been altered, the zero crossings have not been doubled, the two examples are exactly the same except that the 44.1 example has sampled the wave 100 times and the 96k example has been sampled 220 times. In fact the zero crossing falls exactly at the same spot on the timeline at .0034 seconds on both sample examples. The original frequency determines the amount of zero crossings per second, not the sampling rate.
Can you clarify what you mean by 96k having twice the zero crossings?  


index.php/fa/1386/0/
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------Ronny Morris - Digitak Mastering------
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Ronny

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Re: 88.2 & 96k playback problem
« Reply #18 on: July 31, 2005, 04:17:43 pm »

Here's the 96k 10k tone at -6dB. The squares represent each sample in time.

index.php/fa/1387/0/
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Chris Cavell

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Re: 88.2 & 96k playback problem
« Reply #19 on: July 31, 2005, 04:38:55 pm »

The clocking signal has twice the zero crossings...not the data transmitted along that clocking signal.
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Ronny

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Re: 88.2 & 96k playback problem
« Reply #20 on: July 31, 2005, 06:38:13 pm »

Chris Cavell wrote on Sun, 31 July 2005 16:38

The clocking signal has twice the zero crossings...not the data transmitted along that clocking signal.



Ok, I think I understand what you are saying.
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------Ronny Morris - Digitak Mastering------
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bblackwood

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Re: 88.2 & 96k playback problem
« Reply #21 on: July 31, 2005, 09:03:17 pm »

Chris Cavell wrote on Sun, 31 July 2005 15:38

The clocking signal has twice the zero crossings...not the data transmitted along that clocking signal.

Precisely.
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Brad Blackwood
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dcollins

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Re: 88.2 & 96k playback problem
« Reply #22 on: July 31, 2005, 11:28:07 pm »

bblackwood wrote on Sat, 30 July 2005 04:01


The reason the impedance matters as at higher fs, you're dealing with a 'faster' signal - if the impedance is incorrect, the receiver in the card may still be receiving enough data at the 'slower' rate of 44.1kHz to read it, but be unable to at higher fs...



Isn't this the same as the "Toslink" thread that we slogged through recently?

Aka, "where's the clock?"

The interested can Google "RF transmission lines"

DC


bblackwood

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Re: 88.2 & 96k playback problem
« Reply #23 on: August 01, 2005, 05:59:45 am »

dcollins wrote on Sun, 31 July 2005 22:28

Aka, "where's the clock?"

You have no idea how many times I've almost typed that exact question in this thread already...
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Brad Blackwood
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Chris Cavell

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Re: 88.2 & 96k playback problem
« Reply #24 on: August 01, 2005, 08:56:12 am »

bblackwood wrote on Mon, 01 August 2005 04:59

dcollins wrote on Sun, 31 July 2005 22:28

Aka, "where's the clock?"

You have no idea how many times I've almost typed that exact question in this thread already...



Uh oh... Shocked

(I wasn't around for that one...I can only imagine the confusion that led up to it...or came about because of it)
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