How can I record two audio sources at the same time and create a file where one source is the left channel and the other source is the right channel of a lossless stereo audio recording?
My distro is Kubuntu 12.04 LTS.
My audio source hardware is listed at bottom. Specifically, I believe the two sources I want to record at the same time are:
- alsa_output.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo.monitor/#2: Monitor of Scarlett 2i2 USB Analog Stereo
- alsa_input.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo/#3: Scarlett 2i2 USB Analog Stereo
FYI, this question might be relevant (but I don't understand the command shown there): how to merge two audio input source using avconv
EDIT: this definitely seems relevant, but I am struggling to understand it: http://ubuntuforums.org/showthread.php?t=1962947
My first guess about how to do this is this simple script:
#!/bin/bash
OUTPUT="audio_`date +%Y-%m-%d_%H%M`"
avconv \
-f alsa -ac 2 -i <alsa_output.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo.monitor> \
-f alsa -ac 1 -i <alsa_input.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo> \
-map 0:0 -map 1:0 \
-acodec flac \
-threads 0 \
-y $OUTPUT
I assume I need to replace what is in angle brackets with the correct notation. I have no idea if the rest of the above script is even close...
Here's my hardware info:
$ pacmd list-cards
Welcome to PulseAudio! Use "help" for usage information.
>>> 3 card(s) available.
[snip other cards]
index: 2
name: <alsa_card.usb-Focusrite_Scarlett_2i2_USB-00-USB>
driver: <module-alsa-card.c>
owner module: 6
properties:
alsa.card = "1"
alsa.card_name = "Scarlett 2i2 USB"
alsa.long_card_name = "Focusrite Scarlett 2i2 USB at usb-0000:04:00.0-2, high speed"
alsa.driver_name = "snd_usb_audio"
device.bus_path = "pci-0000:04:00.0-usb-0:2:1.0"
sysfs.path = "/devices/pci0000:00/0000:00:1c.4/0000:04:00.0/usb3/3-2/3-2:1.0/sound/card1"
udev.id = "usb-Focusrite_Scarlett_2i2_USB-00-USB"
device.bus = "usb"
device.vendor.id = "1235"
device.vendor.name = "Novation EMS"
device.product.id = "8006"
device.product.name = "Scarlett 2i2 USB"
device.serial = "Focusrite_Scarlett_2i2_USB"
device.string = "1"
device.description = "Scarlett 2i2 USB"
module-udev-detect.discovered = "1"
device.icon_name = "audio-card-usb"
profiles:
output:analog-stereo: Analog Stereo Output (priority 6000)
output:analog-stereo+input:analog-stereo: Analog Stereo Duplex (priority 6060)
output:analog-stereo+input:iec958-stereo: Analog Stereo Output + Digital Stereo (IEC958) Input (priority 6055)
output:iec958-stereo: Digital Stereo (IEC958) Output (priority 5500)
output:iec958-stereo+input:analog-stereo: Digital Stereo (IEC958) Output + Analog Stereo Input (priority 5560)
output:iec958-stereo+input:iec958-stereo: Digital Stereo Duplex (IEC958) (priority 5555)
input:analog-stereo: Analog Stereo Input (priority 60)
input:iec958-stereo: Digital Stereo (IEC958) Input (priority 55)
off: Off (priority 0)
active profile: <output:analog-stereo+input:analog-stereo>
sinks:
alsa_output.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo/#1: Scarlett 2i2 USB Analog Stereo
sources:
alsa_output.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo.monitor/#2: Monitor of Scarlett 2i2 USB Analog Stereo
alsa_input.usb-Focusrite_Scarlett_2i2_USB-00-USB.analog-stereo/#3: Scarlett 2i2 USB Analog Stereo
ports:
analog-output: Analog Output (priority 9900, available: unknown)
properties:
analog-input: Analog Input (priority 10000, available: unknown)
properties:
iec958-stereo-input: iec958-stereo-input (priority 0, available: unknown)
properties:
iec958-stereo-output: Digital Output (S/PDIF) (priority 0, available: unknown)
properties:
lsusb -v shows the Focusrite_Scarlett_2i2 as:
Bus 003 Device 002: ID 1235:8006 Novation EMS
idVendor 0x1235 Novation EMS
idProduct 0x8006
Here is more info on this hardware:
$ aplay -l
**** List of PLAYBACK Hardware Devices ****
[snip]
card 1: USB [Scarlett 2i2 USB], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
$ arecord -l
**** List of CAPTURE Hardware Devices ****
[snip]
card 1: USB [Scarlett 2i2 USB], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
pacmd list-cardsit lists sinks and sources for each card. Sinks "pass through" the audio on its way to the final destination (e.g., speakers). The source in this case is a device that delivers the audio stream to the sink. My Scarlette 2i2 card has two sources listed bypacmd list-cards. By experimenting with Audacity I confirmed that the monitor source can be used to record my voice (using a high end XLR mic) and the other source can be used to record the interview subject's voice. I want to maintain them as separate but synced audio tracks in one file (like L/R stereo).