— Presented by Andrew Watson N1ACW, as part of the week 37 “call for check-ins” on the Lake Oswego ARES Winlink net. Per Andrew… “This brief look into the Windows sound technology stack is far from all-encompassing – it was designed as a 5-minute how-to/look-under-the-hood article.”
Last week we took some time to think about the interface between the sound card device (Digrig, DRA xx, Signalink USB, etc) and the computer. Precision and understanding the nuances are the key to success. However, I’m sure we’ve all spent more time than we would like getting this connection working. Hopefully, we’re all in a good place with this now.
Talking of technology stacks – we’ll take a peek at the computer’s audio stack. This comprises of a sound card device driver and sound card interface control.
The device driver is the low level layer that interfaces with the sound card hardware. It presents a consistent interface to the Windows audio layer above. Usually Windows has the appropriate device driver installed already and this system just works. How do you know it’s working? Use Windows’s device manager!
I told you last week this tool is your friend. It really helps diagnosing what’s going on with errant sound issues. To access the device manager, search for Device Manager in the Windows search box. You can also type devmgmt.msc into the Windows search bar.
I use the device manager so frequently, I have pinned a link to %SYSTEMROOT%\system32\devmgmt.
If the correct device driver is installed, and it usually is on a modern version of Windows, you should see your sound card under Sound, video and game controllers. Digirig and Masters cards show up as USB PnP Sound Device. Signalinks reveal themselves as USB AUDIO CODEC.
If you do not have a device driver installed, then you won’t see the sound card in the device manager. These are pretty easy to install. Follow the sound card manufacturer’s directions for doing so.
Once the sound card has a device driver layer operating correctly over the top of it, then the Windows sound system should be able to see it. I won’t go into the details about how to set up your Windows audio correctly. However, there are a couple of things that you must be aware of.
When you add a new sound card to your Windows system or if your sound card appears on a different USB port, you get a clean start. This means certain options are enabled that you don’t want enabled. For example, you might use your sound card only on your left USB port. One day, you decide to plug it into the right USB port – and all of a sudden, Windows thinks you’ve installed a new device! Infuriating! Now you have to reconfigure your sound settings again.
The sound setting nearly everyone overlooks is the Windows input (microphone) automatic gain control (AGC). AGC is used try to keep the audio input at a constant level. A varying level can happen when a person is talking into a microphone or VoIP phone handset. As they move away from the mic, the level of their audio input drops off and AGC will boost the gain to bring the level up in the system. We DO NOT want this for our sound card! If you ever see your VU meter pegged to the right in VARA FM and adjusting the knobs or pots on your sound card has no effect – then almost certainly you have AGC turned on. Side note: this can happen with a stock Digirig – the solution will be to enable the attenuating circuit by cutting a track on the board.
So, where is the AGC set? Open the Windows Sound Control (type mmsys.cpl in the Windows search bar). Go to Recording and double-click on your sound card. Click on the Custom tab. Disable AGC.
On the output side – Speakers in Windows parlance – make sure you disable all enhancements and spatial sound.
The other critical thing you must do – otherwise you could be in violation of FCC part 97 is to ensure that the Windows beeps and chimes, Youtube or Spotify audio does not get sent to your sound card connected to your radio! In the Sound control panel, set Sound Scheme to No Sounds and uncheck the Play Windows Startup sound. Don’t forget to click the Apply button! Note that this affects the default sound device, but better be safe than sorry. Re-enable, if you need to, when you turn off your radio.
Andrew – N1ACW