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Old 4th June 2008, 01:43 PM   #1
diyAudio Member
 
Join Date: Apr 2005
Location: Spain
Default different clocks in one DVD player

Hello,

In my DVD player there are at least three differents clocks, each running at a different frequency, according the codes written on them: 27MHz, 25.00MHz and 24.57MHz. Why there are three? Perhaps one is for audio, other for video chips? Among them, is there any "main" or "master" clock, which would be beneficial to upgrade first? Would be enough to upgrade only one? Or are all of them equally important?

Thanks
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Old 6th June 2008, 01:32 PM   #2
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Join Date: Apr 2005
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Please, nobody could help?

Thanks in advance
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Old 6th June 2008, 02:05 PM   #3
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Join Date: Oct 2004
I would be careful upgrading these.
For instance in a STB and possibly DVD player, the 27MHz is often a VCXO and is deliberately made to drift in order to maintain AV sync and video encoding timing characteristics amongst other things.
I'm not sure what the other clocks are for.

Do you know what chipset is being used?
What silicon vendor made them, what chip models are they?
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Old 6th June 2008, 09:14 PM   #4
diyAudio Member
 
Join Date: Apr 2005
Location: Spain
Thank you for your post. According the specs by Denon, the video chips used are:

Silicon Optix Reon chip for de-interlacer and scaler

Dual Discrete Video D/A Converter with 12 bit/216 MHz Video DACs (2 x ADV7320)

and for audio the DACs used are:

Burr Brown PCM-1791A (24-Bit, 192 kHz), with HDCD and the own Denon's AL24 Processing Plus

I hope this helps, but without the DVD2930 service manual I can't be more specific. Can somebody tell me where to find it...?

Best regards
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Old 7th June 2008, 08:25 AM   #5
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I would change the 27mhz one
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Old 7th June 2008, 09:14 AM   #6
diyAudio Member
 
Join Date: Apr 2005
Location: Spain
Hi

Thanks for your comments.

Phil, when you said "the 27MHz is often a VCXO and is deliberately made to drift in order to maintain AV sync and video encoding timing characteristics amongst other things", do you mean that a new improved and perhaps "undriftable" 27MHz clock, like the ones Tentlabs, Dexa or Audiocom sell, could disable or impair the Audio Delay Function on the Denon DVD? This is a function for delaying the audio signal up to 200ms with respect to the processed video signal. Now I'm using the DVD with a standard CRT TV via SCART, but in few months I'll use it with a Plasma screen via HDMI, so there will be a lot of deinterlacing-upscaling processing, and I'm very sensitive to lip synchronization issues. Have you any comments?

Regards
(BTW, sorry for bringing this video stuff here in DIYaudio ;-) )
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Old 7th June 2008, 10:55 AM   #7
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Join Date: Oct 2004
I wouldn't change the 27MHz clock.
By it is often deliberately made to drift, I mean the software in the system deliberately makes this drift, by applying PWM to a VCXO, in order to speed up/slow down the system time clock, in order to control AV sync. SO, making that a fixed frequency may give you issues. If, however, it is a simple clock, and made to drift internally, adding a new clock won't really help much anyway.
This is more of a problem for STBs, but DVDs could be susceptible to the same issue.
Try it, but at best, I don't think it will help.
I think you should look at the clock for the audio DAC, and probably not much else.
You should be able to find the audio DAC datasheet and work out which pin is used for clock, and deal with that.

Cheers,,
Phil
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