Level 2 Audio Requirements

The audio subsystem of a PC satisfying the Level 2 specification includes the following items:

• A CD-ROM driver with CD-DA (Red Book audio) outputs and volume control
• A 16-bit DAC with the following characteristics:
  • Linear PCM (Pulse Code Modulation) sampling
  • DMA or FIFO buffered transfer capability with interrupt on buffer empty
  • Mandatory sample rates of 44.1, 22.05, and 11.025 kHz
  • Stereo channels
  • CPU bandwidth usage of 10 percent or less when outputting audio of 22.05 or 11.025 kHz sample rate, or a CPU bandwidth of 15 percent or less when outputting audio of 44.1 kHz sample rate
• A 16-bit ADC with the following characteristics:
  • Linear PCM sampling
  • DMA or FIFO buffered transfer capability with interrupt on buffer empty
  • Mandatory sample rates of 44.1, 22.05, and 11.025 kHz
  • Microphone input
• Internal synthesizer capabilities with multivoice, multitimbral, six simultaneous melody notes plus two simultaneous percussive notes
• Internal mixing with the following capabilities:
  • Can combine three audio sources and present the output as a stereo, line-level audio signal at the back panel
  • Mixing sources are CD Red Book audio, synthesizer, and DAC
  • Each mixing source has 3-bit volume control with a logarithmic taper