Similar to video standards it is also important to understand audio standards.

Unlike older composite and RGB video signals, audio signals are much better documented, however they are still just as complex if not more so that video signals.

Keeping things basic to start with, audio levels are generally two main levels: microphone (MIC) level and Line level. Unless you are inputting an actual microphone signal into some equipment which would be around 0.001V (1mVpp), all other equipment like the audio output of consoles for example over RCA jacks is Line level.

We need to convert the voltage levels to LUFS to understand the audio range that most receivers expect. But for now, let's just work in voltage levels.

Line level voltage is technically in the range of 0 to 1Vpp (meaning the full top to bottom peaks of the signal should reach 1 volt.

The best way to learn is by example. I have a Famicom hooked up to my PCs 3.5mm audio input, recorded through Youlean Loudness Meter along with an oscilloscope to measure the voltage in comparison to the LUFS.

I hooked up the SNES AV cables right channel to go to the PC, and the left channel to go to the oscilloscope so neither interfered with each other.

The highlighted area in green is the exact time of the loudness meters visible window behind the oscilloscope window.

As you can see the typical audio level is around 1V peak to peak, with the gaps in between and the frequency changing the LUFS value.

The LUFS range is a unit of loudness. LUFS are a measurement of loudness that takes into account how humans perceive loudness, including the tonal balance of a sound. One unit of LUFS is equal to one dB.

LUFS is considered a more accurate standard than decibels.

Overall, it is expected to have audio in the average range of -10LUFS, with peaks that go no higher than 0 LUFS.

As LUFS takes into account frequency, it does mean that 0.5Vpp at 1kHz is very different than 0.5Vpp for 10kHz as you can see below.

The 1kHz at 0.5Vpp is -6.9 LUFS, while at 10kHz (higher pitch) that is -3.5 LUFS, over 3dB more in perceived loudness.

For the purpose of audio analysis and when inspecting retro consoles for good audio levels, if you capture with an oscilloscope at 1ms divisions so you see a fast sample, full volume audio should hit around the 1Vpp measurement for expected good and full audio level.