adiciona áudio do arquivo de reprodução ao fluxo de microfone

Question

Eu preciso adicionar um som ao que o microfone está capturando, é possível? Eu comecei com

man aplay

e descobri que posso fazer

aplay -D PCMdevice filepath.wav

então eu listei os dispositivos PCM com

~$ aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
default:CARD=Device
    USB Advanced Audio Device, USB Audio
    Default Audio Device
sysdefault:CARD=Device
    USB Advanced Audio Device, USB Audio
    Default Audio Device
front:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    Front speakers
surround40:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    Direct sample mixing device
dsnoop:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    Direct sample snooping device
hw:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    Direct hardware device without any conversions
plughw:CARD=Device,DEV=0
    USB Advanced Audio Device, USB Audio
    Hardware device with all software conversions

Mas não consigo encontrar nenhum dispositivo PCM que inclua o nome mic ou captura ou entrada, tudo parece resultado, então acho que isso é uma pista ruim.

Alguém encontrou uma maneira de obter o resultado?