Set sblaster4/8/2023 ![]() ![]() The usual way software uses this feature is to create a seamless digital audio stream using a double buffer. The Sound Blaster triggers an interrupt as before, but then it reloads the sample counter to the original value and continues requesting samples from the DMA controller! The final method, introduced with the Sound Blaster 2.0, is very similar to the previous method, except the ending. The Sound Blaster takes this data and sends it to the audio DAC.įinally, the Sound Blaster ends playback then triggers an interrupt to let the software know that it is done with playback.The data byte gets transferred directly from main memory into the Sound Blaster input register! The DMA controller responds by asserting DACK (DMA Acknowledge) at the same time it places the memory address and memory chip select onto the bus.Notice that the software is not involved at all-just the DMA controller, the Sound Blaster, and main memory. The next operations happen in a loop until all the samples have been played back. The software sends the playback command to the Sound Blaster.It programs an internal timer to generate a DREQ signal at the sampling rate. The Sound Blaster is configured for a particular sampling rate.The DMA controller is set to perform a single transfer per DMA request (DREQ). The software configures the PC’s DMA controller (historically an Intel 8237) with the source address and length.It does require a little bit more work to set up the operation. The other method uses the DMA (Direct Memory Access) controller on the PC motherboard to automatically send samples to the sound card. This timing difference means that the waveform being reproduced doesn’t match the source material, and the difference in voltage sounds like noise or hiss. Because PC interrupts are non-deterministic, the samples don’t occur at precisely the sampling rate. In the interrupt handler, the new sample is calculated and then fed to the sound card for playback.Īlthough it’s a simple method, it produces extra noisy playback to due the timing jitter of the interrupt handler. Software using this method typically sets up a periodic timer interrupt. When you send a data byte to the sound card, it immediately changes the analog signal going into the speaker amplifier. It works a lot like the parallel-port DACs that people used to build in the 80s and 90s, or like the Disney Sound Source. The first is called Direct DAC and it means that the PC software has to feed the sound card each sample at just the right time. There are three methods a Sound Blaster card uses to play back digital audio. You can follow along by looking at the schematic here. Let’s lift the hood and examine how the card does its magic. The Sound Blaster 1.0 was not the first PC sound card, but it was the first to support digital sound, two different types of sound synthesis, MIDI, and a joystick all in one card. Sound Blaster 1.0 Principles of Operation Janu6:14 pm eric Cleverness ![]()
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