Using Python to playback mic input to PC in real-time

Question

I'm trying to use Python to 'mic-monitor', i.e., to playback the mic signal through the headphones in real-time, in addition to any other output signal from the PC.

I can accomplish this by amending my PC's playback settings, but I want to do it with Python, so that I can program a Raspberry Pi to mic-monitor my cheap headset for the PS4.

I can almost accomplish this with PyAudio or sounddevice, but there is a small but significant delay. So:

• Is there a way to eradicate that latency with Python, for example by somehow accessing my PC's inputs more directly?
• Otherwise, why is it not possible with Python?
• Can I somehow configure the Raspberry Pi to mic monitor in the same way as my PC?

Sounddevice code is shown below for reference:

import sounddevice as sd
duration = 5.5  # seconds

def callback(indata, outdata, frames, time, status):
    if status:
        print(status)
    outdata[:] = indata

with sd.Stream(channels=2, callback=callback):
    sd.sleep(int(duration * 1000))

Answer 1

There will always be latency with a computer in-between. Professional audio gear is usually custom built for minimal latency (or it's just analog). To reduce latency you need to record smaller chunks at a time before sending them to the output which does introduce more processing overhead. Using smaller chunks can also at some point introduce more jitter in the signal because the inter-frame latency might not keep up with the sample rate. PortAudio is probably likely able to be configured to have a bit less latency, but you're probably getting a lot of the delay from the OS and audio drivers as well. Here's a page discussing how you can optimize the OS and audio drivers for minimal latency on a Raspberry Pi. PortAudio (the driver behind most python audio libraries), also has a discussion on audio driver latency based on your operating system.

looking at the documentation for sd.Stream, it looks like even if you specify a smaller blocksize, due to the implementation, it may make latency even worse.

There is however an option to specify an exact latency (if a particular delay is desirable) or to achieve a best effort "as fast as possible" by specifying latency = "low" This attempts to take into account the specific hardware you're using, and go as fast as possible.