Some months ago, I bought an Oscium iMSO-104 which attaches to an iPhone or iPad to turn it into an oscilloscope of sorts. My thought was that I could get some vague idea of what was going on with some of my equipment by measuring things. Vague indeed it has been as the main analogue probe is 50 Ohms, making it less than ideal for measuring anything digital and it picks up interference easily, resulting in less than a perfect picture. Here are some measurements I took on a whim of various things. Don't read too much into these graphs as the last time I used an oscilloscope was in elementary (primary) school!
Test wave from an Audiophilleo 1 directly from the socket (white) and with a Canare RCA 75 Ohm cable + adaptor (green). The spurious bumps are from interference and should be ignored. The only thing I think is of note is the slightly rounded shoulder of the square wave after adding the cable.
Square wave output of a digitally generated 1kHz signal from the Chesky Records Jazz sampler.
Audio-gd Phoenix XLR headphone output, 1 channel, volume set at 26.
From my iPhone 4 headphone socket at full volume:
From my iPod Classic 160Gb (original type "fat" model) headphone socket at ~55% volume: