Getting signals into the iPhone [UPDATED June 9, 2009]
[size=12pt]Update, June 9, 2009: The latest audio input/output information, for iPhone and iPod touch devices, is now available on the blog.[/size]
This topic addresses several questions that have been coming in regarding SignalScope on the iPhone.
There are basically four ways to get signals into SignalScope on iPhone:
Update, July 29, 2008: The iPhone 3G can sample the built-in mic at 48 kHz, so the 8 kHz sample rate limitation only applies to first-generation iPhones.[/li]
[li]Headset Microphone. With the headset mic, the sample rate will jump up to 48 kHz. I don't know how flat the mic response is, but even inexpensive electret microphones can exhibit a remarkably flat response. I have measured frequencies over 20 kHz in SignalScope with the iPhone's headset mic.[/li]
[li]Headset Input. The headset input allows for a single channel of audio band data. If you want to use anything other than a headset mic, you'll need an adapter cable. A standard mini-plug (1/8-inch) to RCA A/V cable should work (that's a four-conductor mini-plug on one end and three RCA plugs on the other). The recessed jack on the original iPhone may require another adapter, or modification of the A/V cable. I haven't really nailed down the acceptable voltage range, although the input seems to be expecting a low-level mic signal, so input signals may need to be attenuated before they get to the iPhone. A Type 1 measurement microphone (50 mV/Pa), with a unity gain preamp, seemed to clip the iPhone input very easily (with relatively low sound levels).[/li]
[li]Accelerometer. In SignalScope, the accelerometer is sampled at 100 Hz and currently supports units of "g" (that's gravity, not grams). I don't know how accurate the calibration is--it was calibrated by the manufacturer.[/li]
Notes:
Ben
This topic addresses several questions that have been coming in regarding SignalScope on the iPhone.
There are basically four ways to get signals into SignalScope on iPhone:
-
[li]
Update, July 29, 2008: The iPhone 3G can sample the built-in mic at 48 kHz, so the 8 kHz sample rate limitation only applies to first-generation iPhones.[/li]
[li]Headset Microphone. With the headset mic, the sample rate will jump up to 48 kHz. I don't know how flat the mic response is, but even inexpensive electret microphones can exhibit a remarkably flat response. I have measured frequencies over 20 kHz in SignalScope with the iPhone's headset mic.[/li]
[li]Headset Input. The headset input allows for a single channel of audio band data. If you want to use anything other than a headset mic, you'll need an adapter cable. A standard mini-plug (1/8-inch) to RCA A/V cable should work (that's a four-conductor mini-plug on one end and three RCA plugs on the other). The recessed jack on the original iPhone may require another adapter, or modification of the A/V cable. I haven't really nailed down the acceptable voltage range, although the input seems to be expecting a low-level mic signal, so input signals may need to be attenuated before they get to the iPhone. A Type 1 measurement microphone (50 mV/Pa), with a unity gain preamp, seemed to clip the iPhone input very easily (with relatively low sound levels).[/li]
[li]Accelerometer. In SignalScope, the accelerometer is sampled at 100 Hz and currently supports units of "g" (that's gravity, not grams). I don't know how accurate the calibration is--it was calibrated by the manufacturer.[/li]
Notes:
-
[li]SignalScope currently does not support (sensitivity) calibration of the audio input, or audio signal units other than %FS (percent of full-scale, or clipping, voltage)--
Ben
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Comments
Once again, thank you very much for the software, it is a gift to us OCD techie aficionados.
Oh one more thing, I am going to test the 30-pin connector anyways, if it works I will let you know. I bet you were testing it previous to putting it on the market, I will give it a shot though.
I'm glad you like the software.
Currently, the only supported methods for getting audio data into the iPhone are using the built-in mic, or routing audio through the headset jack. Devices that use the dock connector for audio input (Belkin TuneTalk Stereo, Griffin iTalk Pro, etc), aren't currently supported by the iPhone OS. We have submitted a request to Apple for this type of support, and it sounds like others have, as well.
Regarding screenshots, you can tap the camera icon in SignalScope to capture the current analyzer display, even while it is running. Also, in any app, you can hold down the power button and press the home key to capture a screenshot. In either case, the image is saved to the iPhone's Camera Roll photo album.
Ben
Also while we're on the subject. Has anyone built a pad for this application and if so do you know what attenuation is required to bring a line level signal down to match the sensitivity of the iPod touchs' input?
Ben
Can you confirm, or clarify what the facts are if I am mistaken?
Thanks!
SignalScope, SignalScope Pro, and IOScope can all work with two-channel audio input via third party accessories connected to the dock connector.
The following articles (on the blog) may be of interest to you:
Dock Connector Audio I/O
iPhone Line Input Frequency Response Comparison
Ben