Home > Articles > Programming > Windows Programming

Creating .NET Applications That Talk

Speech processing is an important technology for enhanced computing because it provides a natural and intuitive interface for the user. This chapter explains the Microsoft Speech Application SDK, shows you how to create, debug, and tune a speech application, and how to set up a telephony server.
This chapter is from the book

In 1939, Bell Labs demonstrated a talking machine named "Voder" at the New York World's Fair. The machine was not well received because the voice was robotic and unnatural sounding. Since then, many advances have been made in the area of speech synthesis—specifically in the last five years. Also known as text-to-speech, speech synthesis is one of two key technologies in the area of speech applications.

The second technology is speech recognition. For decades, science fiction movies have featured talking computers capable of accepting oral directions from their users. What once existed only in the thoughts of writers and filmmakers may soon become part of everyday life. In the last few years many advances have been made in the area of speech recognition by researchers such as the Speech Technology Group at Microsoft Research.

Speech-based applications have been slowly entering the marketplace. Many banks allow customers to access their account data through automated telephone systems, also known as Interactive Voice Response (IVR) systems. Yahoo and AOL have set up systems that read e-mail to their users. The National Weather Service (NOAA) has an application that reads the weather.

Speech processing is an important technology for enhanced computing because it provides a natural and intuitive interface for the user. People communicate with one another through conversation, so it is comfortable and efficient to use the same method for communication with computers.

Recently Microsoft released Speech Server as part of an effort to make speech more mainstream. Microsoft Speech Server (MSS) has three main components:

  1. Speech Application SDK (SASDK)

  2. Speech Engine Services (SES)

  3. Telephony Application Services (TAS)

All three components are bundled into both the Standard Edition and the Enterprise Edition. The primary difference between the two depends on how many concurrent users your application must support.

Speech Engine Services (SES) and Telephony Application Services (TAS) are components that run on the Speech Server. The Speech Server is responsible for interfacing with the Web server and the telephony hardware. Web-based applications can be accessed from traditional Web browsers, telephones, mobile phones, pocket PC's, and smart phones.

This chapter will focus primarily on specific components of the SASDK, since this is the component most applicable to developers. The installation files for the SASDK are available as a free download from the Microsoft Speech Web site at http://www.microsoft.com/speech/. Chapters 3 and 4 will expand on the use of the SASDK and will introduce two fictional companies and the speech-based applications they developed.

The Microsoft Speech Application SDK (SASDK)

The Microsoft Speech Application SDK (SASDK), version 1.0 enables developers to create two basic types of applications: telephony (voice-only) and multimodal (text, voice, and visual). This is not the first speech-based SDK Microsoft has developed. However, it is fundamentally different from the earlier ones because it is the first to comply with an emerging standard known as Speech Application Language Tags, or SALT (refer to the "SALT Forum" profile box). Run from within the Visual Studio.NET environment, the SASDK is used to create Web-based applications only.

Speech-based applications offer more than just touch-tone access to account information or call center telephone routing. Speech-based applications offer the user a natural interface to a vast amount of information. Interactions with the user involve both the recognition of speech and the reciting of static and dynamic text. Current applications can be enhanced by offering the user a choice to utilize either traditional input methods or a speech-based one.

Development time is significantly reduced with the use of a familiar interface inside Visual Studio.NET. Streamlined wizards allow developers to quickly build grammars and prompts. In addition, applications developed for telephony access can utilize the same code base as those accessed with a Web browser.

The SASDK makes it easy for developers to utilize speech technology. Graphical interfaces and drag-and-drop capabilities mask all the complexities behind the curtain. All the .NET developer needs to know about speech recognition is how to interpret the resulting confidence score.

Telephony Applications

The Microsoft Speech Application SDK enables developers to create telephony applications, in which data can be accessed over a phone. Prior to the Speech Application SDK, one option for creating voice-only applications was the Telephony API (TAPI), version 3.0, that shipped with Windows 2000. This COM-based API allowed developers to build interactive voice systems. The TAPI allowed developers to create telephony applications that communicated over a Public Switched Telephone Network (PSTN) or over existing networks and the Internet. It was responsible for handling the communication between telephone and computer.

Telephony application development would further incorporate the use of the SAPI (Speech Application Programming Interface), version 5.1, to provide speech recognition and speech synthesis services. This API is COM based and designed primarily for desktop applications. Like TAPI, it does not offer the same tools and controls available with the new .NET version. Most important, the SAPI is not SALT compliant and therefore does not utilize a common platform.

Telephony applications built with the SASDK are accessed by clients using telephones, mobile phones, or smartphones. They require a third-party Telephony Interface Manager (TIM) to interpret signals sent from the telephone to the telephony card. The TIM then communicates with Telephony Application Services (TAS), the Speech Server component responsible for handling incoming telephony calls (see Figure 2.1). Depending on which version of Speech Server is used, TAS can handle up to ninety-six telephony ports per node, with the ability to add an unlimited number of additional nodes.

Figure 2.1

Figure 2.1 The main components involved when telephony applications are received. The user’s telephone communicates directly with the server’s telephony card across the public telephone network. The Third-party Telephony Interface Manager (TIM) then communicates with Telephony Application Services (TAS), a key component of Speech Server 2004.

Telephony applications can be either voice-only, DTMF (Dual Tone Multi-frequency) only, or a mixture of the two. DTMF applications involve the user pressing keys on the telephone keypad. This is useful when the user is required to enter sensitive numerical sequences such as passwords or account numbers. In some cases, speaking these types of numerical sequences might entail a security violation, because someone might overhear the user.

Call centers typically use telephony applications to route calls to appropriate areas or to automate some basic function. For instance, a telephony application can be used to reset passwords or request certain information. By automating tasks handled by telephone support employees, telephony applications can offer significant cost savings.

Telephony applications can also be useful when the user needs to iterate through a large list of information. The user hears a shortened version of the item text and can navigate through the list by speaking certain commands. For example, if the telephony application is used to recite e-mail, the user can listen as the e-mail subjects of all unread e-mails are recited. A user who wants to hear the text of a specific e-mail can speak a command such as "Read e-mail." The user can then navigate through the list by speaking commands such as "Next" or "Previous."

Multimodal Applications

Multimodal applications allow the user to choose the appropriate input method, whether speech or traditional Web controls. The application can be used by a larger customer base because it allows the user to choose. Since not all customers will have access to microphones, the multimodal application is the perfect way to offer speech functionality without forcing the user into a corner.

Multimodal applications are accessed via Microsoft Internet Explorer (IE) on the user’s PC or with IE for the Pocket PC (see Figure 2.2). Both versions of IE require the installation of a speech add-in. Users indicate that they wish to utilize speech by triggering an event, such as clicking an icon or button.

Figure 2.2

Figure 2.2 The high-level process by which multimodal applications communicate with Speech Server. The ASP.NET application is accessed either by a computer running Internet Explorer (IE) with the speech add-in or by Pocket IE with the speech add-in.

The speech add-in for IE, necessary for interpreting SALT, is provided with the SASDK. It should be installed on any computer or Pocket PC device accessing the speech application. In addition to providing SALT recognition, the add-in displays an audio meter that visually indicates the volume level of the audio input.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020