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Old 30th October 2010, 11:55 AM   #1
jkeny is offline jkeny  Ireland
Join Date: Feb 2007
Location: Dublin
Default SPDIF waveform Analysis

Below are two scope shots of SPDIF output from the same device - the only difference between them is a better PS.

The better PS speeds up the rise/fall slope of the SPDIF waveform. About half way up the slope of the line is the decision point. I believe that the faster/steeper slope makes for a more accurate decision point with a better chance of it matching the timing of the decision point of the ADC recording & less variability between decision points. Any anomalies in this timing leads to jitter.

The one with the better PS also sounds better

USB power
Click the image to open in full size.

Better PS
Click the image to open in full size.

The first pic shows a kink on the slope, I believe - could this be the result of a reflection falling on & superimposing on the slope?
The ringing on the top of the waveform also seems to be tamed somewhat in the bottom pic.
What sort of explanation can be used to explain the speed up & this sort of change in the waveform based solely on better power - lower impedance, less noise?

Last edited by jkeny; 30th October 2010 at 12:06 PM.
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Old 30th October 2010, 12:55 PM   #2
sendler is offline sendler  United States
diyAudio Member
Join Date: Aug 2004
Location: ny
Default HiFace?

Is that the HiFace? Have you ever seen this Teralink 24/96 usb converter with ASIO that Gigawork sells for $77.00? The larger package might be easier to mod and an output for I2S is standard equipment.
Native 24bit 96k USB to Spdif I2S Converter for DAC - eBay (item 160473208269 end time Nov-23-10 23:44:54 PST)
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Old 30th October 2010, 02:01 PM   #3
jkeny is offline jkeny  Ireland
Join Date: Feb 2007
Location: Dublin
This unit is also with SY for testing from the beginning of October but he hasn't been in a position to address it yet.

This should answer the accusation against me stated here What can measurements show/not show? "However I doubt that any measurement will ever satisfy your needs. You appear not to be interested in proof at all, but something else entirely.....
You have been offered well reasoned help from very technically competent and friendly forum members which you have dismissed at every turn."
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Old 30th October 2010, 02:01 PM   #4
jkeny is offline jkeny  Ireland
Join Date: Feb 2007
Location: Dublin
Sendler, thanks I look into that!
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