Oversampling - where does it take place? - diyAudio
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Old 19th December 2008, 02:05 PM   #1
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Default Oversampling - where does it take place?

I always though oversampling was a function of the DAC chip.

However, reading some articles on the net has left me confused.

The articles I have read suggest that oversampling takes place in another chip prior to the DAC.

I have previously built a non oversampling DAC using a TDA1543 from diyparadise.com.

I have a Cambridge Audio D500SE and the DAC chip on that has failed - so I want to fit a TDA1543 in it's place - but I'm not sure if this will leave me with a non o/s DAC - the existing DAC chip is a CS4391 - I realise some engineering will need to be done to accomodate this - however I'm willing to try it.

The Cambridge appears to have some kind of reclocking circuit - and as a transport into my homebuilt DAC, it outperforms my Marantz CD17, into the same DAC.

I have not been able to locate a schematic for the Cambridge, but using the factory datasheets for the various chips has enabled me to work some of the circuit out.
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Old 19th December 2008, 05:19 PM   #2
oshifis is offline oshifis  Hungary
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The DAC chip just converts what it gets. If it gets 176.4 kHz, it essentially gets 4 samples within the original 44.1 kHz sampling period. If it gets 44.1 kHz, it is fed with non-oversampled signal.
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Old 19th December 2008, 05:43 PM   #3
jitter is offline jitter  Netherlands
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Default Re: Oversampling - where does it take place?

Quote:
Originally posted by audio_tony
I always though oversampling was a function of the DAC chip.

However, reading some articles on the net has left me confused.

The articles I have read suggest that oversampling takes place in another chip prior to the DAC.
It depends on the funcionality of DAC used. My Nakamichi CD-4 has a AD1865N DAC which gets its 18 bits at 8x Fs from the NPC 5840 digital filter. In this case, the digital filter IC does the oversampling.

My Primare D20 has no separate digital filter, the DAC (AK4324, a 1 bit ΔΣ converter) has a built in 24 bit digital filter. In this case the oversampling takes place in the DAC.

The CS4391 is similar to the AK4324 minus volume control. The oversampling probably also takes place in the CS4391.
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Old 20th December 2008, 08:48 AM   #4
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Default Re: Re: Oversampling - where does it take place?

Quote:
Originally posted by jitter
The oversampling probably also takes place in the CS4391.
Not probably, it does take place in the CS4391.
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