In slmodem debug I get:

ardware PCM card 0 'HDA NVidia' device 6 subdevice 0
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 1
  rate         : 9600
  exact rate   : 9600 (9600/1)
  msbits       : 16
  buffer_size  : 1536
  period_size  : 48
  period_time  : 5000
  tick_time    : 1000
  tstamp_mode  : NONE
  period_step  : 1
  sleep_min    : 0
  avail_min    : 4
  xfer_align   : 4
  start_threshold  : 2147483647
  stop_threshold   : 1536
  silence_threshold: 0
  silence_size : 0
  boundary     : 1610612736
Hardware PCM card 0 'HDA NVidia' device 6 subdevice 0
Its setup is:
  stream       : CAPTURE
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 1
  rate         : 9600
  exact rate   : 9600 (9600/1)
  msbits       : 16
  buffer_size  : 1536
  period_size  : 48
  period_time  : 5000
  tick_time    : 1000
  tstamp_mode  : NONE
  period_step  : 1
  sleep_min    : 0
  avail_min    : 4
  xfer_align   : 4
  start_threshold  : 2147483647
  stop_threshold   : 1536
  silence_threshold: 0
  silence_size : 0
  boundary     : 1610612736
<439.907985> main: startup write: 384...