I believe they use an integrated 8051 for bus interaction.

the sb mixer is one of CT1335 , CT1345, CT1745 IC chips

gdjacobs wrote:

I believe they use an integrated 8051 for bus interaction.

Would it be accurate to say then that the SB 1.0 / 2.0 used a microcontroller as the "DSP" and discretes for ISA bus logic, while the SB Pro and the SB 16 use a microcontroller for bus logic and a custom IC for PCM audio and mixing?

look on page "1-6" of the programming manual
https://pdos.csail.mit.edu/6.828/2018/reading … oundBlaster.pdf

it has nice diagrams for you

LightStruk wrote:

gdjacobs wrote:

I believe they use an integrated 8051 for bus interaction.

Would it be accurate to say then that the SB 1.0 / 2.0 used a microcontroller as the "DSP" and discretes for ISA bus logic, while the SB Pro and the SB 16 use a microcontroller for bus logic and a custom IC for PCM audio and mixing?

Sb 1.0/1.5 had discrete logic and MCU chips, sb 2.0 already had proprietary IC with all logic and Intel 8051 core inside.

As far as I know, the 'DSP' is an 8051 or compatible microcontroller, which is connected to a D/A converter. Then the output is fed into an analog mixer.
On the SB Pro and newer cards, this mixer has digital volume control.

There may be various levels of integration of the circuits.

Anyway, the way the PCM audio works on a Sound Blaster is like this:
The 8051 has an internal timer, and is programmed with a divider value to select the actual sample rate (this is how the SB can basically get 'any' sample rate between 4 kHz and 44.1 kHz).
The 8051 will fetch one new sample at every timer/divider interval, and will send it to the D/A converter. So the D/A covnerter is a really basic circuit (like a resistor ladder), and does not have any kind of clock or timing on its own. It just latches a single value, and will continue to output it until a new value is written to it.
Very basic analog low-pass filtering is applied to reduce the aliasing caused by this method. The SB16 introduced a more advanced low-pass filter that was adaptive to the chosen sample rate.

BloodyCactus wrote:

look on page "1-6" of the programming manual
https://pdos.csail.mit.edu/6.828/2018/reading … oundBlaster.pdf

it has nice diagrams for you

Indeed it does! There's no diagram for the SB 1.0 or 1.5 - perhaps Creative Labs didn't want to remind folks of the fact that they used completely off-the-shelf parts?

SB16 adds some actual FIFO based mechanism between DAC and ADC, but I'm not sure if the MCU still has to manually pass data or there's some hardware doing that job.