According to some sources, a Sound Blaster model CT-1320C is a Sound Blaster 1.5. But according to Creative’s own reference materials (which do contain many inaccuracies and cannot be taken as gospel), the only difference between a Sound Blaster 1.0 and a 1.5 is the presence of C/MS chips which provide Game Blaster compatibility.
For example this card is clearly a Sound Blaster 1.5:
Model CT-1320C, no C/MS chips, case closed. But what then is this one?
That’s another model CT-1320C, but with C/MS chips. According to Wikipedia, 1320C makes it a SB 1.5. According to Creative, C/MS chips make it a SB 1.0. How to tell who’s right and who’s wrong? Fortunately, there is a way.
The answer lies in the packaging. The Sound Blaster 1.5 came in this box:
Notice the small “VERSION 1.5” label in the lower left corner of the box. There can be no doubt that this is a Sound Blaster 1.5.
But what about the other one, the one with C/MS chips? The box looks a bit different:
There’s no mention of any version. But look… “STEREO MUSIC”, “24-VOICE” (a nice way to massively exaggerate while not technically outright lying), and “12-Voice C/MS stereo music synthesizer”. Yep, that’s a Sound Blaster 1.0.
That means the 1320C was shipped from the factory with the C/MS chips installed and not upgraded later. The serial number on the box in both cases matches the one on the card itself, so there’s no doubt the boxes match the respective cards.
The disks shipped with the cards also reflect this. The SB 1.0 disks include C/MS software while the SB 1.5 disks do not.
The bottom line is that a Sound Blaster model CT-1320C can be either a Sound Blaster 1.0 or a Sound Blaster 1.5.
Upgrade or Downgrade?
In case it’s not obvious yet, these old Sound Blasters are an incredibly rare case where upgrading the later version meant in fact downgrading to the older model. In other words, SB 1.5 + C/MS chips = SB 1.0.
By late 1991, more or less every game supported AdLib (OPL2) music and the Game Blaster was considered obsolete. Creative removed the C/MS chips and being the marketing-driven company they were, called the reduced-function product “version 1.5”.
The board layout was the same and because the C/MS chips were socketed, it was trivial to leave them out and offer the chips as a separate upgrade for those few who cared.
For reference, the DSP-1321 chip in the photo is a version 1.05 DSP (some form of an Intel 8051 microcontroller driven by a 12 MHz clock). FM1312 is a Yamaha OPL2 chip and the small FM 1314 chip is Yamaha’s DAC.
For those who think that the dizzying array of Sound Blaster 16/32/AWE models was insanely confusing, rest assured that Creative had an early start and lots of practice.
In order to further blur the lines between the 8-bit Sound Blasters, some of the 1.x boards were shipped with a DSP (Digital Sound Processor) version 2.00, such as the SB 1.5 seen in the photo at the beginning of this article.
The original Sound Blasters had DSP version 1.x which only supported “single” DMA transfers. At the end of each DMA transfer which moved samples to or from the card, an interrupt was signaled; the interrupt handler had to reprogram the DMA controller and send a new transfer command to the DSP. It was impossible to have entirely smooth playback, although with the low-quality 8-bit samples and slow sampling rates the tiny gaps were not terribly noticeable.
For improved quality, Creative implemented “auto-init” DMA where the DMA buffer was read from or written to in an endless loop, signaling interrupts along the way as directed. This enabled software to implement double buffering and glitch-free playback with no gaps.
The newer Sound Blaster 2.0 model (CT 1350) used DSP version 2.01 or later. Besides auto-init, the 2.01+ DSPs also supported “high-speed” DMA with sampling rates up to 44.1 kHz. The 1.x and 2.00 DSPs were limited to about 23 kHz sampling rates. Whether this made any real difference for noisy 8-bit sound cards is questionable, but Creative clearly thought it worthwhile.
To make matters more interesting, the DSP on the old Sound Blasters was socketed (see photo above) and Creative offered DSP 2.00 upgrades to Sound Blaster 1.x owners. Therefore even an older Sound Blaster might be equipped with a newer DSP. What this meant was that software requiring auto-init DMA might or might not work on a Sound Blaster 1.x, depending on which DSP was installed.
Confusing? Heck yes, and that was just the beginning.