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That big mysterious gate array

January 21, 2010

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The one page BASIC SID Benchmark.

How do you make sure the SIDs you bought from Ebay are fully working before giving feedback? Or, you are the seller and you want to claim "100% fully working SID all voices. All Filters guaranteed!" and double check your stuff before you send the chips? How do you make sure the SIDs that are in the old C64 in your dad's basement works before attempting a MIDIBox SID , sammichSID or other similar project? (Or midway through the project your dodgy soldering skills makes you wonder if you just blew out your 50$ SID?) You find certain .sid files sound ODD on your setup and you want to be sure all waveforms of all channels sound good across the entire frequency range? You want to make sure the filters are behaving within tolerance, or you want to quickly compare its frequency response with a third party? or... You are a nerd that does SID research, collect SIDs like Pokemons and compare each of them with scopes and frequency analyzers? A: Sure I'm interest

chipspeech Diary, Part 2

Last summer I spent a good part of my late night research time on Texas Instrument Voice Synthesis Processor (VSP) LPC10 decoding chips. TI made LOTS of these from the late 70s to the late 80s, both for the OEM market and for its own use, under different names. They usually prefixed them TMC or CD for internal use, and TMS for OEM use, but their naming was not always consistent, which leads to lots of confusion. The goal for chipspeech is to playback LPC10 streams coming from any Texas Instrument device/software and to do so in a sample accurate manner. We are very close to that goal, but since I found no less than 8 variants of VSPs - all of which had to be accounted for in my emulation core - I'm convinced in fact, that there may be more. A variant is a unique combination of the following features: Pitch encoding format (5 or 6 bit indexes) Energy ROM look-up table Pitch ROM look-up table K (lattice filter) ROM look-up table Voiced chirp ROM look-up table Variab

SID 6581R3 ADSR tables, up close.

In the center of any SID emulation there is the bare waveform generation, and a very accurate explanation of how the this works internally has been published through an interview with its creator, which can be read here . Fascinating read for any geek head! However some very important details are missing, including the exact maths behind the main ADSR clocking but also its pseudo exponential decay/release stages. It was time to have a look at the SID's DIE itself! This is exaclty what kevtris and Lord Nightmare have done here The SID chip has two obvious ROM based lookup tables on the DIE, for each voice. Here is the bigger one, as described in kevtris's blog entry: I basically just cropped parts of the picture of the chip, which is available here , and placed the bit values on top of it. However the blog post doesnt mention, nor explain the purpose of the second table, which I assumed was one of the "exp" tables, as mentionned in the Yannes Interview:

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That big mysterious gate array

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