My car plays the radio, Sirius and Bluetooth at different volumes when set at the same volume number. My TV the same thing when using different streaming services, some louder than others. Why does the same device volume number not make the volume the same across all broadcasts when that is what I would expect to be the final output control?
In: Technology
A sound signal is basically just electricity which is getting stronger and weaker at the frequency which matches the notes in the music. This signal can be about as strong or weak as it wants, from no movement at all to being able to destroy the electrical circuits.
However, this signal is much to weak to actually move the physical diaphragm in your speakers, so your car/TV has to amplify the signal by a certain amount in an amplifier in otder to move the speaker. This amplification step is what the number is: it’s a representation of how much the car is boosting the sound by before sending it to the speakers.
The different applications in your car all use different devices to produce the sound. Your radio is decoding a signal sent via analog radio waves, Sirius is using a digital signal from a satellite, and your phone is sending a different kind of signal over Bluetooth. None of these signals know they’re being sent to a car, so they all take an educated guess of about how strong to make the sound. The amplifier also doesn’t know what devices are sending the signal, just that it needs to make them louder, and makes an educated guess about how loud they’re going to be.
The TV has a similar problem, which is further complicated by the concept of loudness. Music can generally be thought of as existing at a consistent volume, but television will have a wider variety of sounds. These sounds are being made with many techniques and balanced for the shows with different artistic intent, and all have a different sense of how loud they want to be – again, with no knowledge of what device will be playing them back.
Your volume control is only a multiplier, positive or negative, to the original volume of what you’re playing. The TV/stereo manufacturer has no control over what that original volume was.
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