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Thread: C65 in eBay...OMG!

  1. #71
    Join Date
    Jan 2014
    Freedom City
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    If not for the Vlasouki and all the power outages, the Molvanîans would still be making them.

  2. #72
    Join Date
    Jan 2014
    Western North Carolina, USA


    Quote Originally Posted by KC9UDX View Post
    But is it necessary? What does it give besides rounding error that an extra 48 bits of fractional resolution couldn't accomplish? If you want clipping-less, you need fine resolution, not expanded range. Or go analogue..
    With floating-point audio there is effectively no clip point at the fixed-point 0dB full-scale (0dBFS). You scale the exponent, and go on processing. Most DSP is multiplicative in nature, and with a 24-bit mantissa and 8-bit exponent you have huge dynamic range that a fixed-point representation can't match. It's going to get normalized to some peak level a bit below the fixed-point (exponent=0) 0dBFS (a good standard is -0.1dBFS peak normalization for typical peak-limited and compressed export audio), gain-adjusted to be within the output export format's parameters (I run 24-bit 44.1kilosamples per second stereo for most export; it's a better source for MP3, AAC, or AC3 compressors than 16/44.1k is), dithered, and then sample-rate/depth-converted to meet the dynamic range capabilities of the output format anyway.

    Would the CPU in a machine like the C65 need it for that? Or wouldn't you add a 56000 if you needed DSP? There weren't competing machines doing floating point DSP at that time.
    AMD's 9511 and 9512 chips were available in the late 70's, and while a bit slow for this kind of work they were the state of the art at the time. I have a small book, 'The Microcomputer Builder's Bible,' that has schematics for an S-100 AM9511/12 interface. Much clunkier than what Intel did with the 8087 (still late 70's), or what Zilog had designed for the Z280 in Z-BUS mode, but still workable.

    For a long time, the high-end ProTools DAW used 48-bit fixed-point summing ( ) but even ProTools is now using floating-point summing (64-bit) since modern DSP chips can do it natively (ProTools in its full config includes dedicated hardware DSP resources and doesn't do the DSP on the main CPU).

    So a C65 could have a 'floating-point cartridge' with something like the AM9511 in it (by 1990 there were much faster choices, but the AM9511 is vintage-correct for early Commodore). The cartridge could even have a professional audio interface with 24-bit converters and XLR or 1/4 TRS phone jack balanced +4dBu line level I/O. For CD-quality 16-bit 44.1 kilosample per second stereo audio you need to sustain 176.4 kB per second transfer rates, and this is where most 8-bit machines would have fallen flat.
    Last edited by lowen; November 8th, 2017 at 08:39 AM. Reason: Added a bit of detail on exporting from floating-point to other representations.
    Bughlt: Sckmud
    Shut her down Scotty, she's sucking mud again!

  3. #73


    Well, back to reality, quite a feat for a Commodore machine!, 81.450€ is the winning bid o_O'

  4. #74


    BLOWS MY MIND. Looking at the bidding history, I wonder if the actors actually expected to get that deep in the mud...

  5. #75


    Nearly $95K USD WOW!

  6. Default

    The C128 was best used as a GEOS machine and for playing standard C64 games.

  7. #77
    Join Date
    Jan 2011
    Vancouver, BC
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    Could have been a museum or something I suppose. Definitely won't be me.. if I spent that much on a computer I'd need about as much for a divorce lawyer after!

  8. #78


    And a bankruptcy lawyer, too.
    I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
    Machine room:

  9. #79


    i wonder if an Apple "Mark Twain" prototype would command similar money?


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