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iFi Audio Pro iDSD discussion thread

Discussion in 'Dedicated Source Components' started by jwahl, Jan 26, 2014.
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  1. Khragon
    Please include a table of content with links for all of these posts for us to easily read the entire story.
     
    alphanumerix1 likes this.
  2. iFi audio
    We still have some time left to explain everything. :L3000:
     
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  3. iFi audio
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    alphanumerix1 likes this.
  4. iFi audio
    The iDSD PRO offers the following choices of digital processing:

    I. Direct - Bitperfect
    • Both PCM and DSD signals are not processed in any way.
    • For PCM this is effectively what is sometimes called "non-oversampling" or "zero-oversampling", for DSD it means DSD is retained in the original DSD format and directly converted to analogue without any digital processing.

    II. PCM - upsampling
    • In this case PCM is up-converted to 16 X PCM (705.6/768kHz) using a choice of digital filters (Minimum Phase, Apodising, Transient Aligned) that offer different tradeoffs of time-domain and frequency-domain performance.
    • DSD remains completely unprocessed.

    III. DSD - Remastering
    • In this case all incoming audio (except DSD512) is converted to either DSD512 or DSD1024 as selected, using the filter selected (including Bitperfect, meaning no digital filtering is applied).
    • All the above mentioned digital processing options apply to all sources, including the network audio bridge and AES/EBU & S/PDIF inputs.
    • Inputs other than USB are currently limited to maximum sample rates of 192kHz PCM and DSD(64) via DoP.
    1.jpg 2.jpg 3.jpg

    In the nutshell, when:
    • DSD512 Remaster is selected, then all audio (except DSD512) is upconverted to DSD512.
    • DSD1024 Remaster is selected, then all audio (yes, DSD512 as well) is upconverted to DSD1024.
    The upconversion process allows different digital filters, including Bitperfect (no filter), to be selected.

    4.jpg

    For example, this image shows the screen in DSD Remaster DSD1024 mode with a 44kHz input signal being upconverted to DSD1024 (45.158MHz) using the Bitperfect filter.
     
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    Currawong likes this.
  5. Katie88
    I don't understand how something can be both up-converted and bit-perfect simultaneously. If the signal is up-converted, won't the signal be altered and therefore no longer bit-perfect?

    What am I misunderstanding here?

    Thanks
     
  6. Khragon
    What is the general sound signature for pcm and dsd remastering? Dsd remastering will operate on pcm signals as well?
     
  7. technobear
    There are two settings at play here:

    1) Digital Filter (of which there are 4 settings)

    2) DSD Remastering (of which there are 3 settings)

    These two settings interact.

    The first case is DSD Remastering set to OFF. In this case if Digital Filter is set to Bit Perfect, then you get case I - no upconversion and no filtering. If Digital Filter is set to anything else then you get case II - PCM undergoes integer upconversion to 16x PCM and the selected digital filter is applied.

    The second case is DSD Remastering set to either DSD512 or DSD1024. In this case (III) all PCM undergoes integer upconversion to 16x PCM (I'm assuming it is still 16x here) and then the selected digital filter is applied before conversion to DSD. If Digital Filter is set to Bit Perfect then no digital filter is applied before conversion to DSD.

    The only confusing thing is that the digital filter setting is still called Bit Perfect even though the result is not.

    Keep in mind that only integer upsampling is used so the original samples are still in there after upconversion before a digital filter is applied. In this sense and if no digital filter is applied, the PCM data could still be said to be bit perfect before it is converted to DSD.
     
    EVOLVIST likes this.
  8. Katie88
    Thank you for taking the time to explain that with such clarity.

    There's another thing I can't yet get my head around, and can't find a proper explanation for: I perfectly understand compression a wav file to make an mp3. However, I just don't get how upsampling works. Presumably some kind of opposite of compression, but I don't understand how data, which wasn't there in the first place can be 'fabricated' as it were to create a more HD file.

    I know there's something I'm fundamentally missing in the way I'm looking at this subject, but it would be great if you could explain it as well as you just did with 'bit-perfect' etc.
     
  9. technobear
    Math(s). Lots and lots of math(s).

    Edit: there's a simple description here: https://en.wikipedia.org/wiki/Upsampling

    I used to write software that did similar things using curve fitting, first in desktop publishing and later in mapping to plot circles and ellipses at odd angles on maps. Fun stuff. Lots of trigonometry, Bezier curves, splines, complex numbers and vector algebra. Remember those? Don't worry if you don't. Not many people can get there heads around that stuff. One of the reasons I was able to retire at 45 I guess. I'm not a mathematician though - just an engineer.
     
    Last edited: Jan 15, 2018
  10. iFi audio
    DSD upconversion with the Bitperfect mode on operates without applying any digital filter. The signal is directly modulated into a DSD512 or DSD1024 and a digital low-pass is applied.

    In effect this produces a non-oversampling type signal (with aliases, impulse response etc. matching a non-oversampling DAC), but the actual signal is high order DSD.

    And yes, technobear explained it all spot on.
     
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  11. EVOLVIST
    So that I understand, inputs other than USB - like RJ45 - cannot be upsampled, and all of the settings do not apply? So, if I have a 16/44.1 signal coming in, the iDSD Pro will just play it, but no DSD remastering and no upsampling to 16xCD, correct?
     
  12. technobear
    I can't see anything in what iFi have written to suggest that.
     
  13. EVOLVIST
    Or, is this simply stating that you can input up to 24/192 and DSD64, as opposed to anything higher, for the iDSD Pro to work its magic?

    Frankly, if this is the case, I don't see what would be the benefit of going into the iDSD Pro with anything other than 16/44.1 if one is going to upsample, to DSD1024. I guess one wouldn't get the benefit of going "bit-perfect" with native DSD256 or DSD512, or DXD, but for upsampling PCM (which is most of my collection), in theory, you're still going to get close to the best this DAC can produce I imagine.
     
  14. EVOLVIST
    Will the iDSD Pro have the three-way toggle for Solid State, Tube and Tube+? I know it was stated that it was switchable from solid state to tubes. I simply wondered about the Tube+ feature.
     
  15. technobear
    There's a clue in this picture:

    [​IMG]

    Digital filtering only applies to PCM. DSD is always bit perfect.

    Why would you think there is no benefit to 24/96 over 16/44.1? Both can be remastered to DSD512 or DSD1024. It's like the difference between trying to polish a rock and trying to polish a turd. Starting with 24/192 will give a smoother final result.
     
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