Prints a table mapping Windows volume level (0-100) to dB for the default audio device

volume_test.cpp

// volume_test.cpp: prints a level (0-100) to dB table for the default audio device
// I just built this as a console app in VS2019.
// Original code from https://github.com/shubham-theway/Codes-here-there/blob/master/volctrl.cpp
//
// TODO: error checking, device selection, print more device info, ?

#include <stdio.h>
#include <windows.h>
#include <mmdeviceapi.h>
#include <endpointvolume.h>

int main() {
	HRESULT hr;
	
	hr = CoInitialize(nullptr);
	IMMDeviceEnumerator* deviceEnumerator;
	hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, __uuidof(IMMDeviceEnumerator), (LPVOID*)&deviceEnumerator);
	IMMDevice* defaultDevice;
	hr = deviceEnumerator->GetDefaultAudioEndpoint(eRender, eConsole, &defaultDevice);
	deviceEnumerator->Release();
	deviceEnumerator = nullptr;

	IAudioEndpointVolume* endpointVolume;
	hr = defaultDevice->Activate(__uuidof(IAudioEndpointVolume), CLSCTX_INPROC_SERVER, NULL, (LPVOID*)&endpointVolume);
	defaultDevice->Release();
	defaultDevice = nullptr;

	float min, max, inc;
	endpointVolume->GetVolumeRange(&min, &max, &inc);
	printf("volume range in db: min %f max %f inc %f\n", min, max, inc);

	// store original volume to restore it later
	float original;
	endpointVolume->GetMasterVolumeLevel(&original);

	// cycle through the entire volume range, printing scalar and DB values
	endpointVolume->SetMasterVolumeLevel(min, NULL);
	float cur;
	do {
		endpointVolume->GetMasterVolumeLevel(&cur);
		float scalar;
		endpointVolume->GetMasterVolumeLevelScalar(&scalar);
		printf("%3d %8.2f\n", static_cast<int>(scalar * 100), cur);
		endpointVolume->VolumeStepUp(NULL);
	} while (cur < max);

	endpointVolume->SetMasterVolumeLevel(original, NULL);
	endpointVolume->Release();
	CoUninitialize();
	return 0;
}

I wrote this because I was trying to figure out how much attenuation I needed to match the output of my PC/DAC to my turntable, so I could just mix them passively together. The results from my machine (windows 10, Schiit Modi 3 so I think it's the software volume control) are below. I had been keeping the volume around 50 so I probably need a ~10dB attenuator

volume range in db: min -96.000000 max 0.000000 inc 1.500000
  0   -96.00
  2   -58.17
  4   -48.28
  6   -42.34
  8   -38.08
 10   -34.75
 12   -32.03
 14   -29.72
 15   -27.71
 18   -25.94
 20   -24.35
 22   -22.92
 24   -21.61
 25   -20.40
 28   -19.28
 29   -18.24
 32   -17.26
 34   -16.34
 36   -15.48
 38   -14.66
 40   -13.89
 42   -13.15
 44   -12.44
 46   -11.77
 48   -11.13
 50   -10.51
 52    -9.91
 54    -9.34
 56    -8.79
 58    -8.26
 60    -7.75
 62    -7.25
 64    -6.77
 66    -6.30
 68    -5.85
 70    -5.41
 72    -4.98
 74    -4.57
 76    -4.16
 78    -3.77
 80    -3.38
 82    -3.01
 84    -2.64
 86    -2.29
 88    -1.94
 90    -1.60
 92    -1.27
 94    -0.94
 96    -0.62
 98    -0.31
100     0.00