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Computer Audiophile

mansr

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  1. mansr

    Trolls

    I hope we don't have to go that far.
  2. mansr

    UHQCD

    Neat gadget. Just don't expect it to compare with a "real" scope. For the price, you can't really go wrong, though.
  3. mansr

    UHQCD

    Remember, these tests were done on a Philips CD150 player built in 1985. One would hope that a modern player is less affected by disc differences, not more.
  4. mansr

    UHQCD

    There's nothing like an oscilloscope to set the record straight.
  5. mansr

    Trolls

    And look who gave it an upvote.
  6. mansr

    UHQCD

    What matters in the end is the quality of the clock signal driving the conversion in the DAC chip. This CD player uses a pair of TDA1540P chips running at 176.4 kHz. Conversion is simply triggered by a pulse causing the chip to latch the sample value from a shift register. With the scope delay set to one sample interval, we first look at this signal while the player is idle, feeding the DAC section silence. This provides a baseline against which to compare the same signal while playing different discs. The edges are concentrated around two locations not quite 1 ns apart. A possible explanation for this is that the circuit generating this signal from the reference clock has two paths with different propagation delays. Now on to the test discs, starting with Naxos: DG: UHQCD: With all three discs, there is a distinct blurring of the clock edges. Although the waveform snapshots differ slightly, the histograms are virtually identical, and none of the images exhibit any feature setting them apart from the others. To summarise, the UHQCD produces a clearly cleaner high frequency waveform from the optical pickup. While, the initial recovered clock signal has a little less jitter than that from a cheap CD, it does not differ appreciably when compared to a more expensive disc. By the time the playback process reaches the DAC chip, all differences between the discs are gone. If a UHQCD is produced from a superior mastering, that's one thing. However, buying these discs for the better materials also does appear to be pointless.
  7. mansr

    Robert Levi in Trouble Again

    I hope you're not referring to me. If you're talking about the thread I think you are, I intended for my reply to be polite and factual. It was a perfectly reasonable question to ask. That the answer is simple with a little engineering knowledge does not mean that providing it is in any way making fun of anyone. Nothing wrong with experimentation, even if you don't quite know what you're doing (that's "you" in the general sense). What irks me is when people say engineers, because they are engineers, are clueless, brainwashed, or worse.
  8. Think about what happens if the incoming data rate doesn't quite match the local oscillator. This is not how that chip is meant to be used.
  9. mansr

    Trolls

    https://en.oxforddictionaries.com/definition/irony
  10. mansr

    UHQCD

    Here are some more scope images for your enjoyment. This time I looked at the clock recovered from the raw pickup signals we saw earlier. This clock signal is compared against a reference oscillator, and the rotational speed of the disc is adjusted to maintain something resembling a match. For the scope capture, I set a delay of 10 clock periods from the trigger point in order to clearly visualise the jitter. A histogram at the top shows the time distribution of the zero crossings. First, the same Naxos CD as before: Deutsche Grammophon: UHQCD: The spread seen here is mainly the result of the linear track velocity not being quite constant. Remember, this is by design. The data coming out of this first-stage recovery is buffered and subsequently clocked out using the reference crystal oscillator. The minor variations in the histograms are probably caused by differences in the disc production. At this stage of the playback process, I'd be reluctant to say the UHQCD is any better than the regular DG disc. The Naxos CD, interestingly, has a defined peak at both ends of the histogram, not that it affects anything.
  11. mansr

    Trolls

    I guess nobody, certainly no side, is entirely innocent. I'm thus urging everybody, regardless of opinion, if you think someone is being a troll, ignore rather than engage. It'll be more pleasant for us all.
  12. The TDA1543 is a low-cost DAC chip from 1989. It was never competitive other than on price, and now it isn't even that. The one thing it has going for it is simplicity. The 8-pin DIP is probably the easiest IC to hand solder. It also requires very few external components and runs off a single 5V supply. The PCM1710U has much better performance specs, but it is also more difficult to solder, being a 28-pin surface mount SOIC package. Even if you use a DIP adapter, there are many more connections to make. You should also consider the differences in available sample rates. The TDA1543 accepts any sample rate up to 192 kHz but does not oversample. For best performance, you will need to use an upsampling software player. The PCM1710U oversamples by 8x but only supports up to 48 kHz inputs. Although you currently only listen to 16/44 material, that may change in the future. Good luck with your build.
  13. I need something that can do a bit perfect capture.
  14. mansr

    Robert Levi in Trouble Again

    That's not physically possible. Oh, wait...
  15. mansr

    16 bit files almost unlistenable now...

    Nobody made a suitable one.
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