this post was submitted on 14 Dec 2023
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No - I know the difference between a DAC and an amp. The Android (or, maybe it's just Google Pixel devices, I can't recall) audio subsystem limits audio output. My phone max. output is about 800mV. I believe they assume all output is going to earphones and they're trying to protect your hearing. This happens even if you're using a USB DAC. But, there is an app called USB Audio Player PRO (the may be others) that can bypass the Android audio subsystem and send output directly to the DAC and thereby get the full DAC output - typically around 2V.
You may know the difference between a DAC and Amp, but you clearly don't understand what I'm trying to say. I'm saying that a DAC doesn't have its own power output. It literally takes a digital signal, and converts it to analog. In order for it to add any power to the signal, it needs to include an amplifier. Otherwise, the signal will always be a little bit weaker due to the power loss from traveling through the DAC. Most DAC units have at least a weak amplifier for this reason, but there are some units that are just a DAC. And the Amp part isn't going to be controlling the digital volume, i.e. changing the system volume on your device. It will operate on its own volume control, so regardless of how limited the output is from your phone, it will still be made louder as it amplifies the volume independently of the phone. A unit that is just a DAC doesn't have any way to amplify the signal it receives, so it will never be able to make it louder.
You said explicitly that the android system will limit the output of any DAC, but that is wrong on multiple counts. The android system will not limit the output of a DAC because a DAC itself just 1:1 outputs an analog signal converted from a digital source so there is nothing to limit. The android system will also not limit the output from an Amplifier because it literally is not capable of that. That's like saying your water faucet can limit how hot your water can get when you boil it on the stove. An Amp increases the power of the signal after it has already left the phone.
I suggest you learn about the difference between line level and speaker level. This article seems to do a decent job:
https://www.electronicshub.org/speaker-level-vs-line-level/
Your boiling water analogy does not fit - water boils at 100°C (depending on air pressure). It's like the digital signal - boiled/not-boiled, on/off, 1/0, etc.
The output of a DAC (Digital to Analogue Converter) is a line level analogue signal and this signal has an amplitude (voltage) that can be controlled. I'm not a software or audio engineer so I don't understand how, but my reading and own testing supports this.
My own simple test: I have a Google Pixel 4a and an Apple USB-C DAC (dongle). If I use headphones connected to either the phone audio jack or the DAC and any "normal" music player I can listen at full volume - it's loud, but far from uncomfortable. If I use USB Audio Player PRO and configure direct hardware access to the DAC I cannot listen at full volume - it's too loud.