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 TONE()
 Sound a speaker tone for a specified frequency and duration
------------------------------------------------------------------------------
 Syntax

     TONE(<nFrequency>, <nDuration>) --> NIL

 Arguments

     <nFrequency> is a positive numeric value indicating the frequency of
     the tone to sound.

     <nDuration> is a positive numeric value indicating the duration of
     the tone measured in increments of 1/18 of a second.  For example, an
     <nDuration> value of 18 represents one second.

     For both arguments, noninteger values are truncated--not rounded--to
     their integer portion.

 Returns

     TONE() always returns NIL.

 Description

     TONE() is a sound function that indicates various program states to the
     user.  These can be error states, boundary conditions, or the end of a
     time-consuming process.  For example, an error state would sound an
     error tone before alerting the user with a message or interactive dialog
     box.  A boundary condition might indicate that the user is attempting to
     cursor past the top or bottom of a column in a TBrowse object.  A batch
     process also might indicate its completion with a sound to alert the
     user, in case the user has turned away from the screen.

     TONE() works by sounding the speaker at the specified frequency for the
     specified duration.  The duration is measured in increments of 1/18 of a
     second.  The frequency is measured in hertz (cycles per second).
     Frequencies of less than 20 are inaudible.  The table below shows the
     frequencies of standard musical notes.

     Note:  TONE() works only on IBM PC and 100% compatible computers

     Table of Musical Notes
     ------------------------------------------------------------------------
     Pitch   Frequency    Pitch     Frequency
     ------------------------------------------------------------------------
     C       130.80       mid C     261.70
     C#      138.60       C#        277.20
     D       146.80       D         293.70
     D#      155.60       D#        311.10
     E       164.80       E         329.60
     F       174.60       F         349.20
     F#      185.00       F#        370.00
     G       196.00       G         392.00
     G#      207.70       G#        415.30
     A       220.00       A         440.00
     A#      233.10       A#        466.20
     B       246.90       B         493.90
                          C         523.30
     ------------------------------------------------------------------------

 Examples

     .  This example is a beep function that indicates that a batch
        operation has completed:

        FUNCTION DoneBeep
           TONE(300, 1)
           TONE(100, 1)
           TONE(300, 1)
           TONE(100, 1)
           RETURN NIL

     .  This example is a tone sequence that indicates invalid
        keystrokes or boundary conditions:

        FUNCTION ErrorBeep
           TONE(100, 3)
           RETURN NIL

 Files:  Library is EXTEND.LIB, source file is SOURCE\SAMPLE\EXAMPLEA.ASM.