Practical Lab: Audio Exploration

Objective

Find every layer of the audio chain on your own PC: the chip, the driver, the services, the engine process, the endpoints and their format. You only look. The one optional step that changes a setting is clearly marked, harmless and has undo steps.

Time: 25–30 minutes
You need: A Windows PC with working sound, and ideally headphones or speakers. No extra software is required.

What to Open

Part 1: Your Audio Hardware (Device Manager and PowerShell)

1A. In Device Manager open Sound, video and game controllers. Write down:

1. The name of your main audio device (for example "Realtek(R) Audio"): ________________
2. Any other audio devices (HDMI/monitor audio, USB headset, Bluetooth): ________________

1B. Right-click the main device, choose Properties → Driver and fill in:

3. Driver Provider: ________________
4. Driver Version and Date: ________________

Click Driver Details. Do you see names like hdaudbus.sys, hdaudio.sys, portcls.sys or a vendor file? Names differ between PCs.

5. Files listed: ________________

1C. Now ask PowerShell:

Get-CimInstance Win32_SoundDevice | Select-Object Name, Manufacturer, Status
Get-PnpDevice -Class MEDIA | Select-Object Status, FriendlyName

6. Does Status say OK for your main device? ________________

Part 2: The Services and the Engine Process

Get-Service Audiosrv, AudioEndpointBuilder
Get-Process audiodg

7. Status of Audiosrv (Windows Audio): ________________
8. Status of AudioEndpointBuilder: ________________
9. Is audiodg listed? (If not, play a sound and run the command again.) ________________

In Task Manager → Details, find audiodg.exe. Play music and watch its CPU column.

10. Does audiodg.exe use a little CPU while sound plays? ________________

In Task Manager → Services tab, find Audiosrv and AudioEndpointBuilder. They show as Running.

Do not stop or restart these services during the lab. Sound would go silent until they run again.

Part 3: Playback Endpoints (Sound Control Panel)

Open mmsys.cpl.

3A. On the Playback tab:

11. How many playback devices are listed? ________________
12. Which one has the green tick (the Default Device)? ________________
13. Is there a different Default Communications Device? (A telephone symbol) ________________

Right-click an empty area and tick Show Disabled Devices and Show Disconnected Devices. (Untick them later if you like; they only change what is listed.)

14. Did any extra device appear? ________________

3B. Start some music or a video. Watch the green bar beside the default device.

15. Does it move? ________________

3C. Select the default device and click Properties → Advanced.

16. Default Format shown: ________________ (for example "2 channel, 24 bit, 48000 Hz")
17. Are the exclusive mode check boxes ticked? ________________

Write the original value down now. You need it for the optional test in Part 6.

Part 4: Recording Endpoints

Click the Recording tab.

18. How many recording devices are listed? ________________
19. Speak into your microphone. Does the green bar move? ________________
20. Properties → Advanced for the microphone: Default Format: ________________

Do not tick Listen to this device unless you wear headphones. You can get a loud squeal (feedback).

Part 5: The Volume Mixer (Per-App Volume)

1. Open Settings → System → Sound → Volume mixer (or right-click the speaker icon and choose Open Volume mixer).

2. Start a video in your browser and some music in a player.

3. How many apps appear with their own slider? ________________

4. Lower one app's slider to 20%. Does only that app get quieter? ________________

5. Put the slider back where it was.

Also, in Settings → System → Sound, look at Output and Input: pick the same device you saw in mmsys.cpl. Click the device name to open its page and look at its format options.

Part 6 (Optional, Reversible): Change the Default Format

This is the only step that changes a setting. It is safe, and undone in seconds.

1. In mmsys.cpl, Playback → default device → Properties → Advanced.
2. Your original format is already written down in step 16.
3. From the Default Format drop-down choose a different option (for example 44100 Hz if you were on 48000 Hz).
4. Click Test. You should hear a short test tone. (If the test fails, undo at once.)
5. Undo: choose the original format again and click OK.

What happened: the audio engine is now converting between the format of your files and the format you chose (sample-rate conversion, Section 3 and Section 5).

What Should Happen

• Parts 1 and 2 show the chip, its driver and the two services, plus audiodg.exe.
• Parts 3 and 4 show your endpoints, the default device, and each device's format.
• Part 5 shows one slider per app (the sessions of Section 3).
• Part 6 shows that the format is just a setting the engine converts to.

Interpretation Guide

Follow-Up Questions

1. Why did the audio chip show up in Sound, video and game controllers and not under Processors?
2. If an app is at 50%, the device is at 50% and the speaker knob is at 50%, what fraction of full volume do you hear (roughly)?
3. Why might a Bluetooth headset appear as two playback or recording devices?
4. In Part 6, who did the format conversion: the app, the driver, or the audio engine?
5. Name three facts from this lab that you could not have learned just by listening.