Faber Acoustical Forum

Faber Acoustical iOS Apps => SignalScope Pro => Topic started by: FaberAST on June 09, 2009, 01:27:31 PM

Title: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on June 09, 2009, 01:27:31 PM
Additional audio input/output information, for iPhone and iPod touch devices, is now available here (http://blog.faberacoustical.com/2009/iphone/iphone-os-audio-routes/).
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: xpressive-works on June 09, 2009, 05:13:17 PM
If i understand things right, some additional hardware is needed to get an audio-signal into iPod touch via the dock. Is there (or will there be) any possibility (e.g. some driver) to route the audio-signals to the USB-Connector cable?
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on June 10, 2009, 10:31:38 AM
Quote
Is there (or will there be) any possibility (e.g. some driver) to route the audio-signals to the USB-Connector cable?

What exactly do you mean? Where would the signals go once they reached the USB cable?

In other words, what are you hoping to accomplish?
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: Kent on June 21, 2009, 12:26:24 PM
Ok, I'm confused.  Using a iPhone 3gs I want to send signal generator out and use the built-in mic with the octave analyzer simultaneously.  If I use a standard doc output or the earphone output, the signal is routed directly back in to the corresponding input.  To equalize speaker system, I need to be able to output pink noise while using the analyzers simultaneously.  Is this possilble?  Maybe with the Alesis ProTrack?  Thanks in advance!
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on June 22, 2009, 11:28:06 AM
Kent,

If you plug a stereo cable into the headset jack, the selected output will be headphones and the selected input will be the built-in microphone. The headset input won't be selected unless you connect a suitable load to the input channel of the headset jack (which requires a four-conductor mini-plug).

However, based on some measurements (http://blog.faberacoustical.com/2009/iphone/iphone-dock-and-headset-io-frequency-response/) I made on June 19 (see the blog (http://blog.faberacoustical.com)), I don't recommend using anything other than the dock input (line input) of the iPhone 3G S for frequency response measurements (unless you don't care about frequencies below 200 Hz).

You could use the Alesis ProTrack or the Tunewear Stereo Sound Recorder for line-in, but you would still need to use the headset/headphone jack for output. (http://blog.faberacoustical.com/2009/iphone/dock-connector-audio-io/ (http://blog.faberacoustical.com/2009/iphone/dock-connector-audio-io/))

The new demo video (http://www.faberacoustical.com/Downloads/movies/iphone/SignalScope_Pro_EQ/index.php) shows SignalScope Pro making frequency response measurements on a 2G iPod touch (you can see the low frequency roll-off, which is due to the iPod touch headset I/O).

Ben
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: Kent on June 22, 2009, 12:17:10 PM
Ben,  thanks for your response.  At first I could not reconcile your first paragraph as the application would not select mic input with signal generator going out the headset jack.  However, I tried sliding the stereo (tip/ring/sleeve) connector out a fraction of an inch and behold, the expected behavior manifested itself.  Just what I needed.  Must be something shorting if the connector is not seated exactly right.  Thanks again.  Kent
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: gadzby on October 11, 2009, 06:32:22 PM
I would like to use SSP for equalizing my car audio system.  My iPhone (original) connects to the car system using a dock connector -  I have no aux jack input.  Ideally I would use SSP to generate pink noise to the dock output while simultaneously capturing input from the Apple headset microphone (original version), or another mic attached to the headset jack.

I performed a simple experiment to see if this might be possible.  I first setup my iPhone to produce music  on the Apple headset, then connected the car's dock connector.  At that point the desired result was achieved, i.e., the music switched from playing on the headset to the car's stereo system.  But I am unable to determine if the Apple headset micrphone could be tapped by SSP in this configuration.  Would this work, or would the iPhone input also be switched to the dock?

Of course the other option would be to play a CD containing pink noise from my CD player while capturing input using the headset mic.

Grant
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on October 12, 2009, 09:48:56 AM
Grant,

The iPhone will prevent you from using the headset input and the dock output at the same time. However, if your goal is to use the 1/3-octave spectrum analyzer for equalization, then it may be just as well to play pink noise from a CD, as you suggested.

The original iPhone has the flattest frequency response on its headset input, so I would recommend the ThumbTacks (http://www.switcheasy.com/products/ThumbTacks/ThumbTacks.php) microphone for your setup.

Ben
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: gadzby on October 12, 2009, 11:29:46 AM
Thanks Ben for the reply.  So it appears Apple allows the dock input to be used simultaneously with the headphone jack output, but not the other way around.

Thanks for the pointer to ThumbTacks.  Should this microphone be oriented vertically for EQ measurements?

Grant
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on October 13, 2009, 09:07:49 AM
Quote
So it appears Apple allows the dock input to be used simultaneously with the headphone jack output, but not the other way around.
That's right. The iPhone (and 2G iPod touch) can tell the differences between headphones (or a stereo connector) and a headset (a four-conductor connector). When the headset is used, input and output are routed through that single jack. If headphones are used, the iPhone looks for input from another source, so you can use dock input and headphone output.

Quote
Thanks for the pointer to ThumbTacks.  Should this microphone be oriented vertically for EQ measurements?
The microphone is omnidirectional, but the iPhone (and your hand) will obviously affect that. A vertical orientation, then, should be fine.

Ben
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: ubxf on October 15, 2009, 06:31:14 AM
Hello,
Sorry if it has been discussed but would it be possible to use a usb mic with the iphone
Thanks
francois
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on October 15, 2009, 09:12:19 AM
Quote
would it be possible to use a usb mic with the iphone
The iPhone is not a USB host, so a USB mic can't be used as an input source.

Ben
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: ubxf on November 01, 2009, 10:37:43 AM
Thanks Ben,
i've been trying to do an analog line in into the iphone dock connector but it's not working. line out
is working fine though but needed some jumper between pins besides the documented output pins.
Is there an undocumented trick to make the line in work?
Thanks
francois
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: gadzby on November 12, 2009, 11:28:44 PM
Hi Ben:

Can you provide some nominal Ref. Input Level and Input Sensitivity calibration settings for the Thumbtack and Apple earbud/mic devices?

Also, what is the input dynamic range for Thumbtacks and line input?

Thanks,
Grant
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: gregn on December 06, 2009, 11:54:35 AM
It was noted on the blog that the Belkin TuneTalk Stereo works with an iPhone 3GS running OS 3.0.1.  Is it known to work under OS 3.1.2?

I had a MacAlly iVoiceIII working on an original iPhone running OS 3.0.1, but when I upgraded to 3.1.2, I received two errors messages.  After the second one was displayed stating that "This accessory is not supported by iPhone", the device was disabled.  I observe the same behavior on a 3GS running OS 3.1.2.

I'm considering trying a TuneTalk with SignalScope Pro, but would like some assurance that it will work before I purchase it.
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on December 07, 2009, 09:08:07 AM
Quote
It was noted on the blog that the Belkin TuneTalk Stereo works with an iPhone 3GS running OS 3.0.1.  Is it known to work under OS 3.1.2?
Yes.

Quote
I'm considering trying a TuneTalk with SignalScope Pro, but would like some assurance that it will work before I purchase it.
It works fine. In fact, the TuneTalk is now the device I typically recommend.

Ben

Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: gregn on December 07, 2009, 11:13:25 AM
Thanks Ben for the fast response.  I look forward to checking it out.

Greg
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: Simon Logan on February 16, 2011, 01:48:09 PM
Hi Ben,

I've discovered an affordable dock solution for the ipod / iphone that has line in and line out facilities : the Djtech rec-in. I've tested this and both the iphone 3GS and the ipod touch 2G are happy to play music through the line out, and record voice memos via the line in.
However, signalscope pro won't recognise it as a line output device. When you plug it in, it briefly appears as "dock output" in the signal generator before changing to "receiver" (iphone) or "speaker" (ipod).
Do you know why this isn't being recognised? I have ensured that "prefer speaker output" is off.

Thanks,
Simon
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: FaberAST on February 17, 2011, 08:49:24 AM
Simon,

Some devices, including the Alesis ProTrack, do not support simultaneous input and output--these devices were designed for classic iPods rather than for iOS devices. It's possible that this is also true of the DJ-Tech device.

Ben
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: Simon Logan on February 17, 2011, 04:03:25 PM
Thanks for your response Ben.

That may indeed be the explanation. I'll do some tests on the unit anyway and report back.

Simon
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: Simon Logan on March 12, 2011, 03:13:05 PM
Hi everyone,

I wrote a review of the DJ-Tech REC_iN device. I haven't seen any rules saying external links aren't  allowed in this forum, so here it is:
http://diyaudiotest.wordpress.com/2011/03/12/using-the-dj-tech-rec-in-as-a-line-input-device-with-signalscope-pro/ (http://diyaudiotest.wordpress.com/2011/03/12/using-the-dj-tech-rec-in-as-a-line-input-device-with-signalscope-pro/)
I hope someone finds this useful.

Simon
Title: Re: Getting signals into and out of the iPhone and iPod touch
Post by: bvanl on June 22, 2015, 04:57:21 PM
I realize this thread seems to be a bit dusty now, but it is still relevant as I've seen others out in the web refer to it.  Since I'm new to the FaberAcoustical products I too found it useful, but have collected additional information which may make interfacing to an iOS device less fuzzy.

Apple Headset Input / Line Output Jack (3.5mm 4 pole TRRS)

None of this is verified other than seeing a schematic for my MacBook Pro and by empirical measurements of both my iPhone5C and MacBook Pro.

Various headset jacks comply with 1 of 2 standards, CTIA or OMTP. 
1. The Cellular Telephone Industries Association (CTIA) or American Headset Jack (AHJ) standard.  This is used by products from HTC, recent products from Sony and Nokia and Apple devices.  Although, Apple accessories use a patented signaling protocol which is likely not compatible with accessories from other manufacturers. 

2. The Open Mobile Telecommunication Products (OMTP) standard.  This is used by most mobile phones, most Samsung SmartPhones and older products from Sony/Ericsson and Nokia. 
However, the OMTP ceased operations and was eventually absorbed by the Groupe Speciale Mobile Association (GSMA) in 2012.

As technology moves forward, it is unknown how long this information will continue to be accurate, or even relevant.

Standard      “CTIA”            “OMTP”
Contact      Signal            Signal
T   Tip      Left Output / HP         Left Output / HP
R   Ring1   Right Output / HP      Right Output / HP
R   Ring2   Ground / Common      Microphone
S   Sleeve   Microphone         Ground / Common
Clearly, differing accessories are not compatible.  Also, Apple products further differentiate themselves by using Apple’s patented signaling.

A simple resistor connected between R2 and S seems to trick my iPhone 5C and my MacBook Pro into thinking an External Mic is attached.  A resistance between 300 and 10,000 ohms seems to do the “trick.”  When this resistance is somewhere above 10K or below 300 ohms, the device will turn off the Mic Bias voltage.  (My iPhone 5C still powered the mic bias with a 12K resistor, and my MacBook Pro turned off the mic bias somewhere around 275 ohms.  I didn’t bother checking further.)

For my particular MacBook Pro (MBP);
There appears to be isolation inductors in the signal paths at the jack.  The series resistance of the one in the Mic signal input path seems to have a nominal 1K ohm resistance and the ones in series with each of the output signal paths appear to have a nominal 220 ohm resistance.  Measurements I made of the output level capabilities of the output driver (open circuit vs a known load) confirm this 220 ohm series resistance.

The “T” tip connector of the device has a switch contact and the “S” sleeve has a separate sense contact.  The sleeve has separate DC and AC circuit paths / functions.

From quickly reading one of many patents and observing the action of my MBP;
The Mic Bias voltage seems to be applied only after a valid accessory has been detected.  The apple device determines when a plug is inserted into the jack by sensing the tip switch.  The apple device also determines if the plug is only a 3 pole (TRS headphone only), or when it is a compatible 4 pole TRRS accessory.

After a plug has been detected, the device applies the Mic Bias voltage which flows through a series 2,200 ohm isolation resistor and the afore mentioned inductor, and then monitors the state of the applied Mic Bias DC voltage.  If the voltage is outside of the design limits, it turns off the Mic Bias voltage.

The device senses the Mic Bias voltage right after the 2,200 ohm series resistor, and this sense path does not include the isolation inductor mentioned above.

The mic audio signal (AC) has 2 or 3 different paths. One is the load of the series bias voltage components (2,200 resistor, plus the afore mentioned inductor) and a 4.7uF bypass capacitor to ground (at the DC bias source).  Another consists of 3 components in parallel to ground (1nF, 15pF, 100,000 ohms).  The remaining path is not completely known, but is the AC coupled input to the ADC.

The Mic Bias voltage is controlled by an IC which is powered by a 3.3V supply and has an I2C bus connection.  Depending upon the DC load of the Mic, or in the case of measuring several different resistances, the expected output of this IC won't seem to be higher than about 2.8 volts or lower than about 2 volts.  This is calculated from actual measurements across external resistances and then applied to internal components as indicated by the schematic of my MBP.  These values may not be entirely precise, but are hopefully less speculative than some of the information I've seen out on the web (not from FaberAcoustical though).