DTMF Tone on IOS 13 issue

As a matter of interest I did a test by calling another phone nearby and then listening to that phone while I pressed various numbers on the iPhone. Despite the iPhone earpiece feedback seeming to indicate a very short tone when you press a number key on your iPhone, the reality is that the length of the tone that actually goes to line is in fact close to 0.5 of a second which I would have thought would be adequate.

So that means that there are systems out there that require a longer tone length and for that reason I believe that the length of time you press the button should result in the tones being transmitted for that same length of time rather than being hard coded to be limited to 0.5 of a second.

Oh and as an aside, "LTE,VoLTE Off" makes no difference to the time the tone is transmitted that I can tell. It's still around 0.5 of a second. The LTE,VoLTE setting allows you enable or disable the ability to make voice calls and still use Mobile Data simultaneously but a side effect has probably aided you which is great.

There is no real fix until Apple increases the duration to 70/80ms. I have shared my thoughts with Sr. Tech support. You might get some relief if you turned OFF wifi calling. At 50ms there id no room for error detecting the tones. 70/80ms is a very useful value for Apple to consider.

Here is a more user-friendly description for those who find the RFC mentioned above a bit dense:

WirelessMoves Blog: VoLTE – Some Thoughts on DTMF

A commenter there sums up the situation nicely:

…

Many people are not aware that in 3GPP technology DTMF tones are transferred via commands instead of just transmitting as a DTMF tone over the speech channel. Reason for this is that the speech codecs are optimised for speech and not for tones, the codecs would simply mangle the tones. Analogue to VoLTE and even in GSM, a speech frame is dropped in order to submit the DTMF commands in “real time”, i.e. DTMF was and is sent via the FACCH.

Thank you for the possible solution. I saw that in the thread and tried each solution listed, to include that and ensuring the newest update, prior to posting my frustration. It did not resolve the issue. The resolve found with the neighbor’s phone was the ability to press the key and have the tone remain to be recognized. It seems to be the tone length as mentioned by many others.

I am on Verizon and have two 7+ phones that are identical. One sends a recognizable DTMF and the other doesn't. I have no idea why. Both are on the latest version of IOS 13+. This is really weird and I have scoured both phones for different settings that might be a clue.

1. If your touch tone application doesn't respond to the iPhone's tones (or, to be more precise for most carriers now, the tones it regenerates) that's not Apple's problem.
2. You are speaking to fellow users here, not Apple.

To complain to Apple, use this link.

JeremyLeeDiaz wrote:

EEEEEEEEEEEEHHHHHHHK. WRONG.

Its absolutely Apple’s problem because my last iPhone worked fine and my Android phone opens it fine. Which means it’s either this phone or the most recent update(s).

Some light reading:

In GSM and UMTS networks things changed and DTMF start and stop indications were transmitted as signaling messages to be interpreted and converted into a real tone in the network. In VoLTE, things have again been implemented differently.

VoLTE actually uses a mix of analog in-band and digital signaling messages. Instead of sending a message to the other end to produce a tone over the signalling path, VoLTE embeds the signaling message in the RTP (Real-time Transport Protocol) media flow by replacing RTP speech packets with RTP DTMF signaling messages. Usually 20 ms of speech data are contained in each RTP packet that is sent over UDP. Therefore to send DTMF tones, a DTMF signaling message has to be sent every 20 milliseconds instead of a voice packet. GSMA IR.92 points to 3GPP TS 26.114 Annex G which in turn points to RFC 4733 for the details.

When the RTP DTMF signaling messages arrive at a terminating VoLTE device, it’s the device’s responsibility to produce an audible tone for the user. If the terminator is not a VoLTE device, a media gateway is required to transcode the speech path into a codec suitable for the terminating network and the terminating device. As a consequence the media gateway is then responsible to convert the RTP DTMF messages into an audible tone and to inject it into the speech path data stream.

https://blog.wirelessmoves.com/2016/06/volte-some-thoughts-on-dtmf.html

Or, the iPhone doesn't directly transmit a DTMF tone to the other side of the connection, it transmits a tone the cellular network recognizes as a DTMF tone, encodes as a data packet marking it as such, and the remote side of the connection is responsible for generating the DTMF tone your phone sent.

If you really want to deep dive, RFC 4733 is a great place to start.

Try this yourself on most carriers: call a landline and tap a sequence of keys on your iPhone; what you will hear on the other end is no matter what speed you tap, what comes out the other end will be a sequence of defined length tones and spaces.

In fact, if you tap like crazy and enter many digits, like forty or so, you will hear tones and breaks on the other end for several seconds after you stop tapping keys on your phone, indicating the network is generating the tones and breaks.

Short DTMF not working properly for me either. I had a critical business call today with my bank (one of the big ones) and could not get the challenge/response security system to accept the ‘#’ key.

Work around Woz hack: I picked up my old POTS office phone and held the receiver (speaker) up to the iphone12 Max Pro microphone. The bank system recognized the DTMF with no problem.

This needs to be fixed!

Win W wrote:

Android users have no issues!

Are you sure about that?

Most of the issues being experienced here are due to DTMF regeneration on the part of cellular carriers; Apple can't control that.

You can tell if this is occurring by calling a friend or a landline and entering a bunch of tones.

If no matter how fast you enter them on a keypad they come out uniformly short and evenly spaced, DTMF regeneration is being done by your carrier.

Again, you can read more about that here:

https://discussions.apple.com/thread/250764240?answerId=253371576022#253371576022

Hmmm. I'm open for suggestions too! I would love to try your solution but my iPhone 11 doesn't show the same options you mention. I can turn LTE on or off but have no LTE,VoLTE option. Turning LTE off in Atlanta works until one gets into suburbs and the cellular drops to E which is basically useless!

So in my case if I place a call to my ivr system the tones work fine. If I receive a call from the same system the tones do not work nothing I have read here works to fix it. In short same system same phone same carrier dtmf works on out bound calls does not work on in blind calls iPhone 12 pro iOS 14.2.1

Update: while switching off VoLTE solves the problem on my iphone 7, my wifes iphone does not have the problem in the first place and works fine with VoLTE turned on.

Shutting off LTE enablement did the trick! Thanks.

Is the Jitterbug on LTE?

I understand DTMF is more common on LTE than 4G networks, and if so you may want to try shutting off LTE on your iPhone.

Interesting. Both of our 7’s worked... the new iPhone X’s don’t work.