esm —
ESS Technology Maestro 2/2E PCI Audio Accelerator audio device
  driver
esm* at pci? dev ? function ?
audio* at audiobus?
The esm device driver supports sound cards based on ESS
  Technology Maestro, Maestro-2, and Maestro-2E PCI AC97 Audio Accelerator chips
  (ES1968 and ES1978). Due to their power management capabilities, the Maestro
  chips are often used in laptop and notebook systems.
The Maestro is a full-duplex device that allows independent
    playback and recording at sample rates between 4000 Hz and 48 kHz. The sound
    processor is capable of handling and converting 8 and 16 bit mono and stereo
    data.
The esm device driver appeared in
  NetBSD 1.6.
Currently, this driver only supports 16-bit mono recording; an unknown bug
  causes stereo recording to miss a channel. Also not supported yet are hardware
  volume settings, MIDI, and joystick input.