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DTMF not as good when using SPA514 hands free

Level 1
Level 1

We are using SPA514G (firmware 7.5.7) and we have notice that DTMF are not recognized properly by Asterisk when using the speakerphone.

DTMF is set to auto on the Cisco side and RFC4733  in Asterisk. Asterisk will sometimes not read the DTMF correctly when entering the mailbox password. If they use the handset, it works every time. Has anyone come across this strange behavior?

3 Replies 3

Dan Lukes
VIP Alumni
VIP Alumni

It's rather expected (although not welcomed) behavior than surprising/strange behavior.

Speakerphone mode require accoustic echo suppression to be turned on. It may cause distortion of signals. Moreover, AES is susceptible to background room noise. Even not so loud noise make things worse. It apply to all models and all vendors.

Sometime it can be tweaked a lot, but it require depth-in  analysis of the reason the Asterisk is not recognizing DTMF in your particular case.

Generally, speakerphone mode needs to be considered as low quality substitute only. If you wish for hands free operation, use headset.

But even if you will make it work - it's not so good idea to shout your password loudly, isn't it ?

Sometimes I miss the old days when everything just work, never thought DTMF would give me such a hard time. When you think about it, there is no perfect way for IP telephony to handle DTMF.It might be why they have so many way to process it (Info,Inband,RFC, and so on).

I'll advise my users to use the handset I guess.

Thanx for answer.

I also remember those days with no issues caused by DTMF. There has been just no DTMF. Rotary dialing, public switch full of stepping switches ...

Well, it seems I'm slightly older than you ... ;-)