DTMF vs Speech enabled IVR: an in-depth examination

I have recently been heavily involved in a rather large scale deployment of a new customer care IVR system which is gradually replacing an old DTMF-based system. Based on that experience I would like to elaborate a bit on the differences between DTMF-based and speech-recognition-based systems and highlight some concerns that have came up while deploying the speech-enabled IVR. Since there are a lot going on in such systems to make them work, this text will span more than one post.

The system we worked on is an Avaya Media Processing Server (MPS) IVR (a recent acquisition by Nortel) powered up by Nuance speech recognition engine, however the concepts discussed below should apply to a large degree to any platform.

The characteristics of DTMF

Let’s start with DTMF and its characteristics; DTMF is a powerful way of entering and transmitting information through telephony that has been with us for many decades. It has a lot of advantages that made it prevalent in IVR systems up until very recently, with the two most important being the following:

• DTMF is very simple to implement. It reuses the same technology as classic telephony and it is very simple to integrate into branching logic on the IVR platform. It is also very quick to process, relying on the telephony infrastructure already in place.
• It is very accurate. If the user is slightly focused, accuracy can be easily close to 100% despite external conditions such as noise.

Despite these advantages, DTMF does also come with a bunch of drawbacks that really limit its potential:
DTMF is limited in capacity. You can enter so many distinct tones as there are buttons in the phone keypad. While this is sufficient for entering numbers either as data or as options for branching logic, DTMF is incapable of allowing the user to enter more complicated and detailed pieces of information. This severely reduces the capabilities and services that can be deployed.

Excessive use of branching logic in large menus with many submenus makes the IVR application extremely clunky. Menus that contain more than 3-4 different options are too cumbersome for the user. Navigation is also time-consuming, since for example to reach a service that lies in the third layer of an application, the user has to go through three menus with various options each. This can result in slow servicing times.

Finally, using DTMF requires the user having free hands to push the buttons. This is not very helpful when you are on the move or otherwise engaged.

The characteristics of Speech Recognition


On the other side of the table, there is speech recognition. It is a relatively old technology that has only recently reached maturity. Speech recognition systems effectively solve the major problems DTMF suffers from; they allows for very complex input options (not just numbers), they offer vastly superior navigation options and can be used without involving one’s hands. Furthermore, speech-enabled systems feel more natural to interact with. On the other hand, their accuracy is usually a lot less than 100%, performance can be severely affected by noise and they are currently a lot more expensive and complicated to deploy, compared to DTMF.

While initially it seems that it is a more or less an equal tradeoff of pros and cons between the two options, the truth is that speech recognition systems are far superior, assuming a minimum application complexity. The main reason is that most of the drawbacks they come with (which are the strengths of DTMF) simply don’t matter enough! This is a very bold statement that will be extensively discussed in a follow-up post with examples.