[pulseaudio-discuss] sample rate and format for module-echo-cancel (not urgent)

[Per Gunnarsson]

Hello!

I bought a microphone (MICO from Trust) and plugged it into the 3.5 jack
of my computer.

My OS is Debian testing on an old Acer desktop.

To begin, I had a lot of static noise which was removed when I tried:

pactl load-module module-echo-cancel aec_method=webrtc

without really understanding what I did.

I have looked into pactl list and see this:

Source #2
        State: RUNNING
        Name: alsa_input.pci-0000_00_14.2.analog-stereo
        Description: Built-in Audio Analog Stereo
        Driver: module-alsa-card.c
        Sample Specification: s16le 2ch 48000Hz
        Channel Map: front-left,front-right
        Owner Module: 8
        Mute: no
        Volume: front-left: 21845 /  33% / -28.63 dB,   front-right:
21845 /  33% / -28.63 dB
                balance 0.00
        Base Volume: 5841 /   9% / -63.00 dB
        Monitor of Sink: n/a
        Latency: 2301 usec, configured 66666 usec
        Flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY
        Properties:
                alsa.resolution_bits = "16"
                device.api = "alsa"
                device.class = "sound"
                alsa.class = "generic"
                alsa.subclass = "generic-mix"
                alsa.name = "ALC662 rev1 Analog"
                alsa.id = "ALC662 rev1 Analog"
                alsa.subdevice = "0"
                alsa.subdevice_name = "subdevice #0"
                alsa.device = "0"
                alsa.card = "1"
                alsa.card_name = "HDA ATI SB"
                alsa.long_card_name = "HDA ATI SB at 0xfeb40000 irq 16"
                alsa.driver_name = "snd_hda_intel"
                device.bus_path = "pci-0000:00:14.2"
                sysfs.path = "/devices/pci0000:00/0000:00:14.2/sound/card1"
                device.bus = "pci"
                device.vendor.id = "1002"
                device.vendor.name = "Advanced Micro Devices, Inc.
[AMD/ATI]"
                device.product.id = "4383"
                device.product.name = "SBx00 Azalia (Intel HDA)"
                device.form_factor = "internal"
                device.string = "front:1"
                device.buffering.buffer_size = "384000"
                device.buffering.fragment_size = "192000"
                device.access_mode = "mmap+timer"
                device.profile.name = "analog-stereo"
                device.profile.description = "Analog Stereo"
                device.description = "Built-in Audio Analog Stereo"
                alsa.mixer_name = "Realtek ALC662 rev1"
                alsa.components = "HDA:10ec0662,10258100,00100101"
                module-udev-detect.discovered = "1"
                device.icon_name = "audio-card-pci"
        Ports:
                analog-input-front-mic: Front Microphone (priority:
8500, not available)
                analog-input-rear-mic: Rear Microphone (priority: 8200,
available)
                analog-input-linein: Line In (priority: 8100, not available)
        Active Port: analog-input-rear-mic
        Formats:
                pcm




Source #7
        State: RUNNING
        Name: alsa_input.pci-0000_00_14.2.analog-stereo.echo-cancel
        Description: Built-in Audio Analog Stereo (echo cancelled with
Built-in Audio Analog Stereo)
        Driver: module-echo-cancel.c
        Sample Specification: float32le 1ch 32000Hz
        Channel Map: mono
        Owner Module: 31
        Mute: no
        Volume: mono: 21845 /  33%
                balance 0.00
        Base Volume: 65536 / 100%
        Monitor of Sink: n/a
        Latency: 9221 usec, configured 66666 usec
        Flags: HW_MUTE_CTRL LATENCY
        Properties:
                device.master_device =
"alsa_input.pci-0000_00_14.2.analog-stereo"
                device.class = "filter"
                device.intended_roles = "phone"
                device.description = "Built-in Audio Analog Stereo (echo
cancelled with Built-in Audio Analog Stereo)"
                device.icon_name = "audio-input-microphone"
        Formats:
                pcm

Now I wonder why there is a difference in sample specification between
the sources.


Without echo cancellation:

Sample Specification: s16le 2ch 48000Hz


With echo cancellation:

Sample Specification: float32le 1ch 32000Hz


Regards,

Per Gunnarsson