+OLD CS1 Posted January 18, 2015 Share Posted January 18, 2015 With the Commodore 64's open address architecture it was easy to graft on a second (or more, given the completely un-decoded I/O space at $DE00 and $DF00) SID chip I have also seen projects to give a second sound chip to other computers of the era. Has anyone ever worked on giving the 4A a second 9919? My guess is it would take removing the existing 9919 and replacing it with a board with the logic to grab accesses to one of the "shadow" addresses. That is at least one option. Quote Link to comment Share on other sites More sharing options...
+mizapf Posted January 18, 2015 Share Posted January 18, 2015 Should be possible. You'd have to take pin 14 of U506 and lead it to another 2-4 decoder which you can supply with two more address lines A6 and A7, which would give you 4 addresses 8400, 8500, 8600, 8700. 1 Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted January 18, 2015 Share Posted January 18, 2015 The Forti Card puts four of them into the PEB to provide a quadrophonic output. . . 2 Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 18, 2015 Author Share Posted January 18, 2015 The Forti Card puts four of them into the PEB to provide a quadrophonic output. . . Ooooooo nifty. How prolific is this card? Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted January 18, 2015 Share Posted January 18, 2015 Unfortunately, it is relatively rare--but as it is a TI card and I have one, it would be possible to do a new layout for it (and the schematics are available too). I also seem to remember that there was a set of instructions out there at one point in time to build one on a Willforth Prototyping card. 2 Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 19, 2015 Author Share Posted January 19, 2015 It sounds interesting. Do you have any information on how it works, like is it CRU or directly addressable, have a ROM, things like that? Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted January 19, 2015 Share Posted January 19, 2015 It is directly addressable. The current software to drive it is written in FORTH. . . Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 19, 2015 Author Share Posted January 19, 2015 I found a couple of postings from 1990 about the Forti. Nothing technical, but neat to discover that the card was actually designed by TI. It is directly addressable. The current software to drive it is written in FORTH. . . Even more cool. Although I wonder if this kind of card would be interesting versus Marc's SID card. I would not mind having both in my system. I would be happy with just a second 9919, but having four additional available could render some pretty cool and complex stuff. Quote Link to comment Share on other sites More sharing options...
briantw Posted January 26, 2015 Share Posted January 26, 2015 Does anyone remember the Forte card? It had 4 sound chips on a card, giving you 12 tone channels and 4 noise channels! Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted January 26, 2015 Share Posted January 26, 2015 It's the card I've been discussing here with OLD CS1--I have one, although the name is Forti as opposed to Forte. It was a neat idea that was released too late by TI to get any traction, as most of them were sold as DIY kits, not as assembled cards, so that really limited the potential market. Quote Link to comment Share on other sites More sharing options...
briantw Posted January 26, 2015 Share Posted January 26, 2015 Sorry, missed the prior discussion - I was browsing on a phone with a cracked screen. Forti, eh? Time for some googling Quote Link to comment Share on other sites More sharing options...
Gazoo Posted January 26, 2015 Share Posted January 26, 2015 Here's another idea. There were 2 different sound chips used in the TI. Piggyback the different one on the original with the exception of the audio output pin. Run that output to the 2nd channel of a stereo. The output might be different enough to be audible. It would be an interesting experiment, if nothing else. Gazoo 1 Quote Link to comment Share on other sites More sharing options...
ti99iuc Posted January 27, 2015 Share Posted January 27, 2015 yes, i lot for real this idea ... i'd love the possibility to create music by a tracker on the TI99 like was protracker for the .MOD on the commodre Amiga too ... Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 27, 2015 Author Share Posted January 27, 2015 Here's another idea. There were 2 different sound chips used in the TI. Piggyback the different one on the original with the exception of the audio output pin. Run that output to the 2nd channel of a stereo. The output might be different enough to be audible. It would be an interesting experiment, if nothing else. Gazoo Too bad we have no control over individual oscillator phases. A long time ago I experimented with simple surround sound with my Amiga by starting with exactly inverted samples in opposite channels. Then I would vary the offset of one of the channels to produce a sound in the rear speakers depending upon which channel leads or follows the other. The whole project was inspired by a circuit I found in a magazine -- I think it was "Audio" or maybe a "Popular" something-or-other, and managed to piss off the editor ("aroused the ire of" was the exact response) by asking to reproduce the circuit in a user-club newsletter submission. Anyway, the circuit was pretty simple: the positive output of the left and right channel went to the respective speaker, then the negatives of the two speakers were connected. Pretty simple yet worked very well. (IIRC, the article also went into detail about using a variable resistor on one or both sides of the circuit to control displacement, but I cannot recall exactly.) 1 Quote Link to comment Share on other sites More sharing options...
Willsy Posted January 27, 2015 Share Posted January 27, 2015 Two independant sound chips, one on the left channel and one on the right channel isn't really, strictly speaking, stereo. I know what you mean, and I'm really splitting hairs here (apologies) but two systems, one on the left, and one on the right is just two mono systems. It's only really stereo (and again, I *do* apologise for the pedantry) if you can place the channels in the stereo spectrum. For that, you would need a (minumum) two channel mixer on the sound card that is controllable from a couple of I/O ports or a memory-mapped address. Then you could pan/sweep the channels left and right, or place them in various positions. Ideally, (say) 8 single channel sound chips would be great, into an 8 channel mixer. You would have 8 individual channels that could be placed anywhere in the stereo spectrum. That would be seriously cool. If the devices were capable of playing samples of a reasonable quality you'd have a heck of a drum machine. Quote Link to comment Share on other sites More sharing options...
briantw Posted January 27, 2015 Share Posted January 27, 2015 As a kid, I was fascinated by the phasing you'd get from CALL SOUND(4250, 110, 0, 111, 0, 112, 0) for example. I thought, what if you could do that with more channels? So I had my cousin bring his TI over, and plug it into a separate TV. Naturally, I hit 113, 114 and 115 Hz on his, while playing the original on mine, but the results were unspectacular. For that brief moment, however, we did have some stereo going on there Quote Link to comment Share on other sites More sharing options...
TheMole Posted January 27, 2015 Share Posted January 27, 2015 Two independant sound chips, one on the left channel and one on the right channel isn't really, strictly speaking, stereo. I know what you mean, and I'm really splitting hairs here (apologies) but two systems, one on the left, and one on the right is just two mono systems. It's only really stereo (and again, I *do* apologise for the pedantry) if you can place the channels in the stereo spectrum. For that, you would need a (minumum) two channel mixer on the sound card that is controllable from a couple of I/O ports or a memory-mapped address. Then you could pan/sweep the channels left and right, or place them in various positions. Why would you need a mixer on the sound card, when it would be perfectly possible to do this in software? I agree that two sound chips do not a stereo system make, per sé. But I do think it can be used to create stereo sounds, if programmed specifically to do so and output to two different channels, without the need for a hardware mixer with panning controls. Quote Link to comment Share on other sites More sharing options...
Willsy Posted January 27, 2015 Share Posted January 27, 2015 That might work. Certainly the idea is very good. You could have the left and right chips play the same tone at different volumes and that would certainly produce the effect, so yeah. I didn't think of that! Good thinking bat man! Quote Link to comment Share on other sites More sharing options...
Tursi Posted January 27, 2015 Share Posted January 27, 2015 It may not be true stereo in the audiophile sense, but for thirty+ years we've been perfectly happy calling independent channels run to different speakers "stereo" on computer systems. They usually score extremely high separation of the channels. Quote Link to comment Share on other sites More sharing options...
ti99iuc Posted January 27, 2015 Share Posted January 27, 2015 (edited) I Remember for a Dual Sid Project for Commodore 64 ... here i have a friend that have this system and only when the dual sid is supported in the games or demos i can hear the difference (and it is very very nice effect ), otherwise it is a normal C64 audio Edited January 27, 2015 by ti99userclub Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 27, 2015 Author Share Posted January 27, 2015 I Remember for a Dual Sid Project for Commodore 64 ... here i have a friend that have this system and only when the dual sid is supported in the games or demos i can hear the difference (and it is very very nice effect ), otherwise it is a normal C64 audio This is more like what I had in mind. I will have to open up my 128D and show the horribly shoddy job I did implementing the dual-SID (I think I put mine at $D700 as that was the "standard" of the time.) I designed cartridges in 11th grade (1990-ish) which could host eight or 16 SIDs in $DE00. Memory fails, but maybe the 16 chip model was cascaded eight chip units with one at $DE00 and one at $DF00. I remember being very concerned about being REU and SwiftLink friendly. Anyway, the idea of each generator having its own output with a mixer is kind-of neat. That way you could just assign tones in a generator and then select whether that generator goes to left, right, or both. Not practical with what we have available, but a neat idea. Otherwise, each chip or group of chips assigned to each channel is the normal way of doing it. 2 Quote Link to comment Share on other sites More sharing options...
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