Faber Acoustical iOS Apps > SignalScope

Getting signals into the iPhone [UPDATED June 9, 2009]

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Update, June 9, 2009: The latest audio input/output information, for iPhone and iPod touch devices, is now available on the blog.

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:

* Built-in Microphone. When using the built-in microphone, the sample rate is limited to 8 kHz, so you only get about a 4 kHz bandwidth.
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.
* 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.
* 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).
* 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.
* 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)--SignalScope Pro does.

First off, I want to say that software is awesome, thank you very much. Now this is just an idea, you could call this a helpful suggestion. The iphone has really clean audio connections from what I have experienced, but apple has a cable which may work better than using the headphone jack. Now maybe this won't work, and I don't know if you really want to do it, but there is a 30 pin connector that you can plug into the iphone. The one I had was made to cover every input channel to the DVD player HD, and then connect the 30-pin to the iphone. http://store.apple.com/us/product/MB129LL/A?fnode=home/shop_ipod/ipod_accessories/cables_docks&mco=NTQ4OTg That cable is a composite standard A/V cable, that probably could work for what you are wanting to do for input. That could also have the cable from the from the computer for a power source/possible input, into the 30-pin connection line pre-composite hook in. http://store.apple.com/us/product/MB128LL/A?fnode=home/shop_ipod/ipod_accessories/cables_docks&mco=MTM1MTc Now that is the one I have, now maybe you could find something to do with the extra (Pb, and Pr), possibly, I am not sure, I should read up on it, but, maybe that Pb and Pr line could hook into the iphone with the composite sources. Then this could have 2 devices going in at once. I really don't think that is necessary, but hey it is a idea. Maybe that would be useful for a multi channel surround sound setup. I was thinking that the 30-pin connection would provide clean audio to the iphone, vs's a headphone jack. I know I would love the idea of having the option to save a print out/screenshot while measuring an audio level. If you are already at a computer you could just hook it up through another interface though.... All of this maybe unnecessary because you had said you don't know how to hook up through the doc connector, I am not sure if that is a software compatibility issue or if you just did not know how that there was 30-pin A/V cable for the iphone.

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.


Since the release of 2.2 which supposedly allows the use of line in, are there any devices that work?

With iPhone OS 2.2, it appears that the Belkin TuneTalk Stereo works with the iPhone, iPhone 3G, and iPod touch 2G. The Griffin iTalk Pro works with the iPhone 3G. Neither device works with the original iPod touch.


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