109 lines
5.3 KiB
Text
109 lines
5.3 KiB
Text
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reSID was written by Dag Lem.
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The project was started after reading an interview with Bob Yannes, the
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head engineer of the SID chip. This interview was made by Andreas Varga,
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with additional questions from Linus Walleij. The interview can be found on
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the SID Homepage:
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http://stud1.tuwien.ac.at/~e9426444/sidpage.html
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The reverse engineering of the SID chip would not have been possible without
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this interview.
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Also found on the SID Homepage is an examination of the SID noise waveform
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written by Asger Alstrup. This article was of great help in reverse
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engineering the complete algorithm for the noise waveform.
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Lars Haugseth has been invaluable in the testing of reSID.
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In a matter of hours after hearing about my project, he had completed a 6510
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disassembler in Perl. The importance of this was not evident to me until the
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next day when he had disassembled the music routine for "Outrun Remix" by
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Geir Tjelta, made some changes to it, reassembled, and produced a file
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containing 48K of SID register values.
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The first tests of reSID were run on this file.
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With an exceptional memory of Commodore 64 tunes Lars Haugseth has pointed
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out several errors in reSID that are now corrected.
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Morten Rollan and K<>re Gunnar Nesheim have provided interesting and insightful
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information regarding digital filters. K<>re Gunnar Nesheim has also kindly
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provided a 1901 monitor and a C64C from his private computer museum. His C64C
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was used to measure the MOS8580 filter cutoff characteristics.
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VICE has been an inspiration for this project, and testing of reSID has
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been greatly simplified by VICEs -sounddev dump option. Teemu Rantanen
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has written support for reSID in VICE, making it possible to choose at runtime
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between his excellent SID emulation and, given enough CPU power, the reSID
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emulator engine. Tibor Biczo, Andreas Boose, and Andr<64> Fachat have provided
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combined waveform samples for 6581 R1, R3, R4, and 8580 R5 SID chips.
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The VICE home page is found at:
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http://vice-emu.sourceforge.net/
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The author of SIDPLAY, Michael Schwendt, has implemented a patch to link
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libsidplay with reSID. Using his excellent tune player he has pointed out
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several bugs in reSID. He has also provided invaluable information related to
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the bugs as basis for further investigation. Most notably, the infamous ADSR
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delay bug, of which I was previously unaware, has finally been understood and
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is now correctly implemented in reSID. The SIDPLAY home page is found at:
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http://www.geocities.com/SiliconValley/Lakes/5147/
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A bug report from Daniel Lacasse led to the discovery of a previously unknown
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SID bug, the ADSR boundary bug.
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Anders <20>deg<65>rd has explained aspects of analog electronics and audio
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equipment.
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Bob Yannes has patiently answered questions and has provided lots of
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technical information on the SID filter. Thank you Bob!
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Julius O. Smith III has provided much of the theoretical basis for the
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audio resampling with his "Digital Audio Resampling Home Page":
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http://www-ccrma.stanford.edu/~jos/resample/
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H<EFBFBD>rsfalvi, Levente has made a thorough investigation of the DC levels
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in the MOS6581 chip. His results are available in C= Hacking Issue #20,
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and form the basis of DC corrections in reSID. Levente found that each
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voice independently contributes to the DC level in the mixer. Note
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that some of the conclusions in the article are incorrect, as the
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maximum and minimum voice output levels are interchanged.
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The author of SIDPLAY2, Simon White, has given a lot of feedback on
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reSID. Most importantly he found and fixed a bug in the fast clock
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version of the ADSR emulation.
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Laurent Ovaert found and fixed a bug in the fast version of the noise
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register shift routine.
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Andreas Dehmel has reported all sorts of initialization and overflow
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errors.
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Laurent Ganier demonstrated two crucial techniques for vectorizable
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filter convolution in a patch. Firstly, he made the filter elements
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correspond to the sampling frequency, allowing the linear
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interpolation to be factorized out from the convolution. Secondly, he
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duplicated elements in the sample ring buffer, achieving contiguous
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storage of the samples. The current resampling implementation builds
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on these ideas, improving on them by using shifted filter tables for
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generalization and accuracy.
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Otto Jarvinen has made great contributions to SID emulation by
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thoroughly investigating and documenting the effects of the test bit
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on the noise waveform shift register, and the behavior of waveform 0.
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He has demonstrated how the test bit can be used to generate entirely
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new waveforms, and how waveform 0 can be used to generate 8-bit
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samples.
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Michael Huth has made high quality SID die photographs available, and
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Tommi Lempinen has done impressive work revectorizing and annotating
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these die photographs. The current level of accuracy in the emulation
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of the SID filter would not have been possible without the work of
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Michael and Tommi.
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Antti Lankila has worked tirelessly on improving SID emulation in his
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fork of reSID, resid-fp. He has, among other things, measured and
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described the main non-monotonous behavior of the SID 6581 D/A
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converters, measured and analyzed small-signal filter cutoff curves
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for several SID 6581 chips, and is always willing to help with
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analysis in the quest for ever improved SID emulation. He has also
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found and corrected a bug in the reSID resampling code.
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Finally I would like to thank my business partner Stian W. Arnesen for
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putting up with all this nonsense.
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