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Thread: Droid source voltage test (and a few signal generator apps)

  1. #1
    Founding Member earthtodan's Avatar
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    Droid source voltage test (and a few signal generator apps)

    Since I use my HTC Droid Incredible as an MP3 source in the car, I wanted to look at the waveform at max volume to see the voltage and make sure there was no clipping. To do this, I used a Velleman HPS-10SE oscilloscope, and every signal generator app I could find in a couple minutes of searching the Market. I used different apps just in case they produced different results, which they did.

    The battery was recently charged and the media volume was turned all the way up. Note, this is a rooted phone with a downloaded OS from an independent developer (probably irrelevant, yet worth mentioning).

    Here is the test with an app called Signal Generator. It is a simple app that only does sine waves and noise.



    The screen lists the RMS voltage as .359V. Note this is a one-sided reading, in other words, the RMS is actually double that, or .718V.


    Next I tried an app called SoundForm, which is versatile enough to do several different waveforms.



    Curiously, it measured the lowest of all tests. In the above photo, I have the oscilloscope set to peak-to-peak measurement, so now the number looks different. To convert peak measurements of a sine wave to RMS, you multiply by .707. Thus, the RMS voltage this app produced was .590V.


    Next I tried my personal favorite generator, FuncGen. This has the most versatility and the friendliest user interface. It also produced the strongest signal.



    This produced an impressive 1.494V peak to peak, or 1.056V RMS with no measured clipping.

    I also tried some other waveforms just for fun. The square waves were kind of dirty and came out differently depending on how I pushed it.








    Next up is an app called Frequency Generator. This is the most difficult app to use, because the frequency is a digit scroller. You can't enter a number, or get a frequency precisely, or quickly. You can change the waveforms. However, this app has the unique capability of being able to play up to three signals at once. With multiple signals on top of each other, I finally got some clipping, at 1.837V peak to peak.



    I had to turn the volume rocker down in order to get a clean waveform.




    So the question is, what is the max output when playing music? To find out, I downloaded a 0dB 1kHz test tone from Real of Excursion and loaded it up.



    The music player turned out to be the bestest app of all, and put out 1.683V peak to peak, or 1.190V RMS. If you look closely there might be one pixel of clipping, but if you were to plug this phone directly into an amp, I think it would be safe to set your gains at 1V.


    Next goal: harmonic distortion testing. And maybe I'll perform the same tests on some other phone models if I can get my hands on them.

    Dan

  2. #2
    Founding Member OSN's Avatar
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    Excellent, didn't see this here at first. :tomato:

    Would be great if people had phones to donate for testing...kinda attached to mine.

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    Devil's Advocate Adam_MSS's Avatar
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    This is awesome, Dan. I'm impressed with those output levels from a phone.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



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    Founding Member earthtodan's Avatar
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    (Deleted faulty THD graphs)
    Last edited by earthtodan; 11-27-2011 at 10:54 PM.

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    Founding Member earthtodan's Avatar
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    I measured my roommate's iPhone 4S (He's a mac, I'm a PC). For the sake of consistency, I used the same 0dB 1kHz test tone.

    This is the max voltage using the phone's MP3 player. At .989V RMS one-sided, it is 1.978V RMS total, which is pretty impressive.



    Deleted faulty THD measurements.
    Last edited by earthtodan; 11-27-2011 at 10:53 PM.

  6. #6
    Devil's Advocate Adam_MSS's Avatar
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    Yikes. Odd order products are nasty. Very interesting info and a good heads up to droid/iPhone users for where to calibrate gains. If I was using one I'd set it a couple notches below where the distortion appears and tweak the rest of my gain structure to get the output I want.

    Then I'd go into settings/music/volume limit and limit the iPhone to avoid the distortion.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



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    Senior Member cvjoint's Avatar
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    This is really neat. I suppose one could use a smartphone straight into an MS8. I've been contemplating this. One sucky part is that you only get like 10 clicks of adjustability in volume. Despite some of these phones getting really close to 2v it's hardly usable if you want to keep distortion low.

  8. #8
    Founding Member earthtodan's Avatar
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    That is the idea; I am using my Droid as an auxiliary input to my BitOne. The auxiliary input gains are set manually with an input voltage slider.

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    Big Daddy Chad's Avatar
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    I prefer to just use the dock out, just find it better all around. I'd imagine android does not have this though right?

  10. #10
    Founding Member earthtodan's Avatar
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    What does the dock out do?

    There is the possibility that the distortion I'm measuring is the input limit on my computer's sound card, not the output limit on the devices. I'll have to test for that somehow.

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