SweepGen - An Audio Sweep Generator - David J Taylor

SweepGen turns a sound-equipped PC into an Audio Oscillator and Sweep Generator.
In conjunction with audio test instruments, you can make frequency response 
plots.  SweepGen uses the sound card in your PC to produce sinewaves that are 
mathematically correct almost to CD quality, indeed it's more likely that the 
quality of your PC sound card will be the limiting factor rather than the code 
in SweepGen.  If you are interested in programming the sound hardware at a low 
level under Windows, you may find SweepGen's source code helpful in 
understanding the programming techniques involved.


Usage:

Extract SweepGen.exe from the .ZIP file to a convenient location, and run it!
SweepGen uses no other DLLs, or registry entries.  You will be presented with a 
dialog box that is, I hope, self-explantory.


Operating modes:

SweepGen has three operating modes: fixed frequency (with no sweep), a slow 
single sweep lasting about 45 seconds intended for recording onto tape for 
subsequent replay and analysis, and a fast sweep lasting about 0.75 seconds
intended for use with an oscilloscope for direct analysis of a circuit or to
show the effect of any tone controls on your audio board.  

In the fast sweep mode, there is a choice between a continuous or stepped change 
of frequency, the steps allowing easier discrimination on the scope.  Also, 
there is a 3:1 duty cycle to allow the scope to retrace and retrigger.

In both sweep modes, the sweep may be linear or logarithmic in frequency, with 
log being more suitable for examining a broad frequency response and linear more 
suitable for narrow band filters.


Frequency ranges:

You can program any frequency range you want into Sweep, but if you make the 
maximum less than the minimum, you'll only get one frequency!  There is no check 
against programming a frequency in excess of 22.05KHz, so you can note the 
effects of aliasing.

  For convenience, there are four preset frequency ranges called:

      wide:   20Hz .. 20KHz        hf:   1KHz .. 15KHz
    speech:  300Hz .. 3KHz         lf:   50Hz .. 1KHz


Output levels:

Sweep has a choice of fixed output levels selectable from 0dB to -20dB in 3dB 
steps.  There will be a fraction of a second delay between selecting a new 
output level and the actual output changing since, the internal sinewave 
lookup table has to be recomputed.


Reference:

A book that I have found invaluable on digital audio is:

  The Art of Digital Audio, 2nd edition, 1994
  John Watkinson
  Focal Press (an imprint of Butterworth-Heinemann Ltd)
  ISBN 0 240 51320 7


Release History:

1996 June 01  V2.0.0  First public domain released version


Notes:

The program is written with Borland's Delphi 2.0, and full source is included.  
You do not need access to Delphi 2.0 to run Sweep, but you WILL need sound 
hardware on your PC.  The program runs on Windows 95 and Windows NT 3.51/4.0.

Safety notice:  Playing a continuous tone at a high level might damage your 
amplifier, speakers, or hearing.  Please exercise sensible precautions!


Contacting the author:

This program is placed in the public domain, but remains copyright of David J 
Taylor, Edinburgh, 1996.  This program is provided "as is", without any 
support.  Whilst I cannot answer queries relating to the use of this program, 
I'd welcome any comments or suggestions for improvements you may have.


david.taylor@gecm.com
1996 June 01