(Apologies if this is a really obvious question, it's all a bit new for me.)

Hello all

I'm researching ways I can make the sound coming out of the audio jack of a smartphone comparable between smartphone models. For example, I want to pump out a sound of certain energy ("sound power?") at x MHz from an app for, say, a Samsung S5 and an iPhone 6. Within software (Android/iOS) I can set a % volume to output, but calculating dB level is challenging because it's a relative value and you don't really know where 0dB is.

It occurred to me that there must be some device (surely?? :-) ) that I can connect to the audio jack that can measure the actual output after impedance of the hardware within the phone. So the set up would be:

iPhone  --> [DEVICE] --> Headphones
Samsung --> [DEVICE] --> Headphones

Main Question: I don't know if such a device exists, and if it does exist what it would be called?

The idea here is how much measure sound power (a la https://en.wikipedia.org/wiki/Sound_power) is going into the headphones. That leaves interpretation of what 0dB is to the wayside and I can properly compare (and therefore calibrate within software) what % volume I should be using for iPhone and Samsung to output the same energy.

For example I could calculate, on average, that iPhone 6 and Samsung S5 pump out the same sound power at 31% and 33% volume at 1Mhz respectively; I can now use that "calibration" to asses 0 dB through a decent set of headphones via a different investigatory technique (now that I'm sure they're both pumping out the same "volume" level under the same air pressure conditions).


I believe your looking for a form of gain compensation.

Some high end mixers include this and I imagine there's also many software solutions to this problem.

If you were to make an external device for this it would most likely need a dedicated DSP chip to perform the compensation.

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  • Thanks, so I'm guessing such an external device doesn't already exist? – Manish Patel Jul 19 '16 at 20:11
  • 1
    Specifically, you might look into a compressor or limiter. There are many such external (aka "outboard") effects devices on the market. – user9881 Jul 19 '16 at 22:35
  • Compressing or limiting instead of accentuating the signal could cause the sound to not sound the same on the other end. – duFF Jul 20 '16 at 16:25
  • Automatic input trim is a thing that has been around for years. You have it on most cameras and pocket/field recorders. I don't know of any headphone amplifier with that feature though... basically, what it does is apply a basic input gain and it turns it down a little as soon as it detects clipping. – BadgerBadger Feb 15 '17 at 8:22

What you need from what I understand is a mastering. I would strongly advice you to try IK Multimedia - T-Racks. It's a mastering suite with a lots of mastering presets. But you can also master with different and independant plugins.

For example :

  • An equalizer to clean signal.
  • A multiband Compressor/Expander.
  • A stereo Imager.
  • A limiter.
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Such a thing does not exist because it is not practical. You cannot measure "sound power" by observing the voltage (and/or current) out of a device headphone jack. The "sound power" is dependent on the sensitivity of the earbuds or headphones (or speakers) and you have no way to measure or even sense that. So your whole premise seems dead before it even starts.

PS: NO smartphone is going to put out ANY "MHz". Continuing to use that term makes it look like you don't understand what you are talking about. The very highest frequency you could reasonably expect out of a smartphone or any consumer audio device is around 20KHz.

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