Tandy 3 Voice
|Tandy 3 Voice|
The Tandy 3 Voice is an audio protocol used on the Tandy 1000 series of home computers. The audio data is sent from the software to the computer's on-board audio chip. The on-board audio chip is different depending on the model of Tandy 1000 and can be any chip from the 3 Voice Chipset including an SN76496, an NCR 8496, or a PSSJ-3. As the Tandy 1000 is a clone of the PCjr, so too is the Tandy 3 Voice protocol a clone of the PCjr 3 Voice protocol, and so both protocols support three square wave channels and a noise channel.
Here is a list of each model and which chip it used for sound.
|Tandy 1000 Model||Audio Chip||Confirmed By|
|EX||NCR 8496||Visual Inspection|
|HX||NCR 8496||Visual Inspection|
|SL, SL/2||PSSJ-3||Not Confirmed|
|TL, TL/2, TL/3||PSSJ-3||Not Confirmed|
|RL, RL/HD||PSSJ-3||Not Confirmed|
|RLX, RLX-HD, RLX-B, RLX-B-HD||PSSJ-3||Not Confirmed|
|RSX, RSX-HD||PSSJ-3||Not Confirmed|
The different chips gave different results. Since the SN76496 was the chip the system was designed with, it has no known problems. Switching to the NCR 8496 didn't cause any errors, but the audio was slightly different due to the different noise channel. The PSSJ-3, however, introduced a fair amount of problems. Games that tried to set the audio multiplexer to output to the RCA jacks would cause the chip to reset, making it fail to play the next note sent to it (this is noticeable in Sierra's AGI games). Another problem is that the chip can't poll the joystick while playing digital samples, causing missed button presses while sound effects are playing. However, the worst problems are not from the PSSJ-3 chip itself, but rather, how Tandy integrated new technology. The RLX model has both Tandy and VGA graphic capabilities, but defaulted to VGA. Many early games that were developed for both Tandy and non-Tandy platforms would check for the presence of VGA graphics, and, if they were found, not run in Tandy mode, which meant that, even though Tandy audio was present, it wasn't used, and the game would default to PC speaker. Further problems occurred in the RSX and RSX-HD models because the I/O address was moved from 0xC0 to 0x1E0 in order to make room for a second DMA controller. Games published after the release of the RSX model required users to specifically choose their Tandy model, but any game released prior to the RSX had to be patched in order to recognize the new address, but since few were, most games would not play music at all on the RSX models.
Also, since some games use multiple audio devices for music, some songs will play below an A-1 note. Since the Tandy 3 Voice did not contain frequencies lower than an A-1, notes lower will be replaced by an A-1, providing inaccurate sound playback.
The Tandy 3 Voice protocol is emulated in DOSBox, however, it currently only emulates the SN76496 chip. This isn't much of a problem, since each chip is compatible with the others, but it won't accurately play the nuanced noise differences.