When we mute our phones, do the apps actually stop sending the data to generate sound at the speakers?

Since Android has system-level volume control, changing volume in Android seamlessly changes the volume so other apps don’t have to worry about it. So if you mute using the Android UI, the apps are still running as normal, but the audio passes through a system-level mixer before being played over the speaker. Muting is really just a toggle for zero volume that remembers the last volume you had it at.

Short answer is yes the apps send audio data (unless they have options to customize volume or muting, etc), but the OS controls overall volume.

An app could be written to check to see if it’s muted and if so avoid processing sound, as long as the OS underneath provides access to volume information.

There’s still data moving, but audio is one of the least taxing things you will ever ask a computer to do.

44KHz, 16-bit sound? 88Kb/s per channel, 176Kb/s for stereo. It’s pathetic. The processor can do that in idle and barely bother waking up, because it just shoves it into a buffer and processes it all in a fraction of a second. Audio is mainly “waiting for the speaker to be ready for the next byte”, and it’s incredibly slow by modern computing standards.

There’s still thousands of data streams being processed by a phone all the time, but they don’t result in anything and can be done in fractions of a second and then put back to sleep. Hell, if nothing else, it has to listen out for text messages, Internet data, phone calls, Bluetooth devices that you usually join to it, button presses, swipes, fingerprint activation, etc. Some are catered for by specialist chips but those chips are doing just the same – waiting for the data stream to indicate that something needs to be done, and then “interrupting” the main CPU to get it to do something with the data.

Somewhere in any modern machine there are probably dozens of audio channels playing away to themselves (even if they’re just sending 0 constantly), they’re mixed and send to a variety of destinations (speakers, headphone, Bluetooth, the apps themselves to send up to Facebook or whatever). Your Windows machine has a channel for each program running, in effect, so you can make your browser quieter than your movie without having to adjust the central system volume, and so on.

But if the volume is down, or off, or the device missing then the stream just gets mixed and then… nothing happens to it. It might be that the speaker is just sent zeroes, or that it’s actual power is disconnected (depending on the type of speaker), but it makes no real difference in terms of power anyway. A headphone cable is probably only 1V peak-to-peak at it’s loudest, and an internal speaker isn’t far off, and a Bluetooth speaker is separately powered and it’s the radio signal to it that costs power.

But no different to the stream off data coming off your touchscreen even though you’re not actually pressing anything – it gets sent, filtered (so specks of dirt aren’t mistaken for fingers), processed, converted to a suitable format, and sent on their way. It’s probably only “off” when the phone is locked, but even then it has to wake up instantly so likely it’s only in a low-power mode rather than actually off.

So many bytes flowing through your phone even on idle for a few minutes that you wouldn’t be able to process them all as a human in a year, most likely. But computers are built for that, and an audio stream is one of the simplest and smallest lots of data of all. Your USB hub (even an internal one like on a phone or laptop) with nothing plugged in communicates hundreds of times faster, using more power, all the time the machine is on.

It’s easier for the phone manufacturer to control volume and have the apps just play an audio signal rather than having apps also controlling phone performance

It’s impossible to say for certain as there are too many apps to account but typically the apps just play music independent of phone volume.

The amp that powers the speakers is being told by the phone to not output any power when it’s muted, that’s it. So yes, the sound data is still being processed, it just isn’t being output since the amp is being told there is no energy (Zero volume).

If you want no audio processing, you would have to disable the drivers. That would theoretically free up resources as it would not be transferring sound data at all even if you made the amp output max power (Full volume)

There is still some data being transmitted to keep the connection active. This is usually called keep-alives or heartbeat signals.