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Upsampling to avoid de-emphasis?
amiti
post May 23 2012, 15:27
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Hello,

My sound card Juli@ uses ak4358 DAC which applies digital De-emphasis for 32, 44.1 & 48kHz sampling rates.

Is it a good idea to upsample 44.1khz files in order to avoid this?
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DVDdoug
post May 23 2012, 17:33
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I'm not exactly sure what that means... De-emphasis is normally used to flatten frequency response when there has been pre-emphasis (boosting high frequencies on the recording). It's used on analog tape and on FM radio. Pre-emphasis is rare on digital recordings, although it is allowed on CDs and CD players will automatically add de-emphasis when needed.

Digital audio is always (or should always be) low-pass filtered to prevent alaising during analog-to-digital conversion and to "reconstruct" the analog waveform during digital-to-analog conversion.

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Is it a good idea to upsample 44.1khz files in order to avoid this?
Upsampling is sort-of like copying a VHS tape to Blu-Ray. It does not improve quality, and in fact there is a teeny-tiny loss of quality (hopefully unnoticeable) in any conversion.

This post has been edited by DVDdoug: May 23 2012, 17:34
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amiti
post May 23 2012, 21:11
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I saw in the DAC chip specifications page de-emphasis applied only for 32 , 44.1 and 48 Khz samplerates. I know upsampling is usually useless but if by increasing the sample rate I will bypass this de-emphasis filter - maybe it would be worth the tiny loss.
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pdq
post May 23 2012, 21:28
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According to the data sheet a de-emphasis filter is available at those sample rates if the applications calls for it. Otherwise it can simply be left disabled.
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lvqcl
post May 23 2012, 21:32
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I'm sure that this function is optional and is off by default.
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amiti
post May 23 2012, 23:39
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OK , thank you for the help.
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Wombat
post May 24 2012, 01:34
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I donīt know if reading datasheets is necessary when using an already build design smile.gif
The chip applies de-emphasis when a register is set to do so. If this chip is used in a CD Player and the inserted CD shows a pre-emphasis flag the internal logic of the CD-Player sets the de-emphasis register and the DAC applies it. Otherwise it stays off all the time.
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