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Old 12th November 2011, 02:46 PM   #1
Kuro is offline Kuro  Hong Kong
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Default How to build a circuit to determine the input sampling rate?

I'm using a Logitech Transporter.

It has two clock circuits. One running at 11.2896MHz and the other one at 24.576MHz. They correspond to the sampling rate of 44.1K and 48K based music playback.

Now I discover that the clocks are both running at all times. And I found that by disabling one clock (say the 24.576MHz one), the sound of redbook playback is significantly better. I believe the two clock circuits are interfering with each other via the Vcc and GND rails.

My question is, is there a way to build a circuit to detect the incoming sampling rate, so that I can use a relay to power on just one clock and leave the other clock powered off?
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Old 12th November 2011, 03:40 PM   #2
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Yup, you can use an arduino to count pulses and then trigger a relay. I am doing something similar where i use an arduino to look at the word clock line and light one of six LED's corresponding to 44.1, 48, 88.2, 96khz etc etc.
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Old 12th November 2011, 03:42 PM   #3
Kuro is offline Kuro  Hong Kong
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What exactly is an arduino?
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Old 12th November 2011, 04:49 PM   #4
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Open source microcontroller

Arduino - Wikipedia, the free encyclopedia

I personally like the chipkit Uno32, it has a faster processor and more I/O pins and is cheaper.

Digilent Inc. - Digital Design Engineer's Source
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Old 13th November 2011, 01:13 AM   #5
Kuro is offline Kuro  Hong Kong
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Originally Posted by Zero Cool View Post
Open source microcontroller

I personally like the chipkit Uno32, it has a faster processor and more I/O pins and is cheaper.
I'm trying to avoid having two clocks with different freqs in the circuit loading on Vcc which produces asynchronous noise, and I certainly do not want another microcontroller with yet another clock loading on the Vcc line.

I'm hoping there is a simpler solution to this...
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Old 13th November 2011, 01:56 AM   #6
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Originally Posted by Kuro View Post
I'm trying to avoid having two clocks with different freqs in the circuit loading on Vcc which produces asynchronous noise
Properly decopling the two clocks would be the way to go. Ferrite beads on each power line, capacitors right on terminals...
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Old 13th November 2011, 02:01 AM   #7
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Originally Posted by Kuro View Post
I'm trying to avoid having two clocks with different freqs in the circuit loading on Vcc which produces asynchronous noise, and I certainly do not want another microcontroller with yet another clock loading on the Vcc line.

I'm hoping there is a simpler solution to this...
Try adding to the decoupling. I had a similar problem with a USB board with noise on the 5 volt rail. A 470nF and 10uF sorted the problem.
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Old 13th November 2011, 02:26 AM   #8
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Without getting into an issue about the decoupling, it should be possible to distinguish between the two clocks pretty easily.

First, I'd buffer both into counters to get lower frequencies to work with, although this is not absolutely necessary. Then I'd build a filter at each frequency. Then I'd use a simple diode detector to develop a DC level from the filtered input(s). Then I'd use comparators to produce logic level outputs when one or the other frequency was active.

Job done.
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Old 13th November 2011, 02:55 AM   #9
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Originally Posted by counter culture View Post
Without getting into an issue about the decoupling, it should be possible to distinguish between the two clocks pretty easily.

First, I'd buffer both into counters to get lower frequencies to work with, although this is not absolutely necessary. Then I'd build a filter at each frequency. Then I'd use a simple diode detector to develop a DC level from the filtered input(s). Then I'd use comparators to produce logic level outputs when one or the other frequency was active.

Job done.
If i read his initial post. BOTH clocks run at the same time!
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Old 13th November 2011, 01:39 PM   #10
Kuro is offline Kuro  Hong Kong
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If i read his initial post. BOTH clocks run at the same time!
I want to disable one of the clocks based on the input sampling rate. So only the clock for the intended sampling rate is active, and the power to the other clock will be disconnected.

I found that by disabling the XO that is not in used, the sonic improvement is rather large.

I'll give the decoupling caps a try, I have some 15uF OsCon and I'll parallel it with the existing ceramic, which I think is 0.1uF (will measure to find out).

But I know the best sonic quality is by disabling the unused XO, not by filtering caps or inductor filtering.
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