# Droid output voltage test (and a few signal generator apps)



## Ludemandan (Jul 13, 2005)

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


----------



## OSN (Nov 19, 2008)

Great testing. I have read that output is usually 1V average. For phones that can be used with a dock, where it outputs to the USB port rather than headphone jack, that's what I'm most curious about, as that's how I use mine. Would love to get digital audio out of the HDMI port, but no luck on a means to do that where I don't have an HDMI display with fiber output.


----------



## t3sn4f2 (Jan 3, 2007)

OSN said:


> Great testing. I have read that output is usually 1V average. For phones that can be used with a dock, where it outputs to the USB port rather than headphone jack, that's what I'm most curious about, as that's how I use mine. *Would love to get digital audio out of the HDMI port, but no luck on a means to do that where I don't have an HDMI display with fiber output*.


An "hdmi to spdif extractor" from company like gefen, startech, Kramer electronics wouldn't work?


----------



## OSN (Nov 19, 2008)

t3sn4f2 said:


> An "hdmi to spdif extractor" from company like gefen, startech, Kramer electronics wouldn't work?


You're right, there are options on the market, but the cheapest I've seen any of these is $160, which is more than I paid for the phone. Should have stated more clearly. :blush:


----------



## Ludemandan (Jul 13, 2005)

There are 15 volume intervals from mute to max. REW measures minimal THD (no bars showing up on the graph at the wrong frequency) up to 4 clicks down from max, or 11/15 volume.


----------



## t3sn4f2 (Jan 3, 2007)

Edited due to OP update edit.


----------



## Ludemandan (Jul 13, 2005)

True that. To be fair, I should probably do these tests with -3bB tones.


----------



## Ludemandan (Jul 13, 2005)

Here is Tool - Vicarious shown in Audacity and magnified. Each marked interval is 1/2 second. -3dB would be the half amplitude line (.5). There is a lot of information above that.


----------



## t3sn4f2 (Jan 3, 2007)

Ludemandan said:


> Here is Tool - Vicarious shown in Audacity and magnified. Each marked interval is 1/2 second. *-3dB would be the half amplitude line (.5).* There is a lot of information above that.


-6dB = .5

Trust me


----------



## Ludemandan (Jul 13, 2005)

I measured my roommate's iPhone 4S. 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.


----------



## Ludemandan (Jul 13, 2005)

Whoops! I realized that the distortion products I was reading may have been my computer's sound card reaching is maximum input level, rather than the devices reaching their maximum output level. 

To test this, I went in to my control panel and turned down the level of the mic input. Then I re-tested with my Droid. At max volume, no harmonic distortion!

I have edited my previous posts to remove the graphs showing distortion. Looks like the Droid can be played at max volume. I'm glad to see this, because I haven't heard anything disturbing when I use it at max input in my car, so my ears agree.


----------



## t3sn4f2 (Jan 3, 2007)

Ludemandan said:


> Whoops! I realized that the distortion products I was reading may have been my computer's sound card reaching is maximum input level, rather than the devices reaching their maximum output level.
> 
> To test this, I went in to my control panel and turned down the level of the mic input. Then I re-tested with my Droid. At max volume, no harmonic distortion!
> 
> I have edited my previous posts to remove the graphs showing distortion. Looks like the Droid can be played at max volume. I'm glad to see this, because I haven't heard anything disturbing when I use it at max input in my car, so my ears agree.


Thank god, you had me questioning my iphone 3gs measurements when I saw your 4S results. 

Here's an excellent site to reference for this type of stuff.

NwAvGuy


----------



## Ludemandan (Jul 13, 2005)

I'll read that when I have time. 

My first clue was how the THD products suddenly sprang up out of nowhere, like they hit a ceiling. I know that a non-sinusoidal waveform is actually just a sum of many sin waves, so I thought, maybe those odd-order distortions are what clipping looks like. However, my second clue was that the oscilloscope shows a clean sine wave all the way up to the top. It's a pixelated screen, but it ought to show a dirty waveform if those distortion products are really there.


----------



## Wattser93 (Mar 12, 2010)

When listening to regular music, the iPhone seems to clip at about 3/4 volume. Does the o-scope confirm that?


----------



## Ludemandan (Jul 13, 2005)

I have heard what you are talking about in the higher frequencies, but I haven't found it on the 'scope. I'll play around with it some more when I get the chance. The iPhone belongs to my roommate.


----------

