Listening to audio discs on your Mac's internal CD drive can be a pretty flat experience- the hardware lacks the features of even modest stereo systems.  Digital Equalizer is a shareware program which addresses this problem.  It allows you to sculpt the tonal quality of an audio signal according to your listening tastes.

Version 2.0 adds several enhancements to the interface.  The key addition is a more conventional, logarthmic scale, allowing fine control over the musically important lower frequencies.

This documentation file is divided into fifteen sections:

(1) What It Does And How It Works
(2) The Controls
(3) Other Features
(4) Quickstart Examples
(5) System Requirements
(6) A Word About Sluggishness
(7) Registering
(8) Updates
(9) Distribution
(10) Known Conflicts / Problems
(11) Comments / Suggestions / Bug Reports
(12) Disclaimer
(13) Thanks
(14) Mathematical Notes
(15) History

(1) What It Does And How It Works

Digital Equalizer records sound from the internal CD drive (or other source), filters it according to an adjustable curve, then plays the resulting signal through the Mac's speaker and/or headphone jack.

It can run in the background, meaning you can still use your favorite CD Player program to play audio tracks.  Registered users can choose to have Digital Equalizer automatically launch a player.  The equalizer can also accept sound from external sources, through either the sound input jack or AV connector.

I recommend that you skim at least the next two sections before using Digital Equalizer. For users who want step-by-step instructions on how to use this application to listen to audio CDs or sound from external sources, check out the fourth section, Quickstart Examples.  

(2) The Controls

The Digital Equalizer interface features four sets of controls:

• Big Graph  The big graph depicts the current filter function.  You can change the shape of the curve by either clicking and dragging the pegs one at a time, or by double clicking in the graph and tracing the desired shape with the mouse button still down.  The shape of the curve specifies the percentage of sound energy allowed to pass through at the frequencies listed along the bottom of the graph.  The vertical axis goes from 0 to 100 percent (or from 0 to -30 dB, see below), and the horizontal axis goes from 0 to  22 kilohertz (if you're playing at the 44 kHz rate), or from 0 to 11 kilohertz (if you're playing at the 22 kHz rate).  You can set the scale of each axis by choosing Curve Prefs… from the Equalizer menu.  You can set the color scheme of the graph from the Equalizer menu.

• Square Buttons  The four square buttons give you control over four aspects of the equalizer's signal processor. Successively click on a given square button to toggle its state. From the left, the square buttons are:

     - Player [On/Off]  When the player is on (green arrow in button), sound is
      piped from the input source to the output device. If the equalizer is active
      (see next button), the signal is filtered according to the Big Graph before it is
      played. If the equalizer is inactive, however, the signal is played as-is. When
      the player is off (green stripes in button), sound is not piped to the output
      device, whether the equalizer is active or inactive.

     - Filter [Active/Inactive]  When the equalizer is active (wavy line in
      button), the signal is filtered according to the Big Graph (see above) before it is
      played. When the equalizer is inactive (flat line in button), the signal is not
      filtered before it is played.

     - Input Source [Microphone/Internal CD/AV Connector]  Choose the
      equalizer's audio source using this button.  There are three choices, each
      represented by an appropriate icon on the button's face.  For more information
      about choosing an input source, see the QuickStart Examples section.

     - Rate: [44/22 kHz]  This button lets you select the play rate.  Choose 44 for
      maximum fidelity but heavier CPU burden, or 22 for reasonable fidelity but less
      CPU overhead. When set to 22, the equalizer cuts off frequencies above 11 kHz.
      This sounds drastic, but in practice the signal degradation is usually
      imperceptible, and can lighten the microprocessor's load appreciably.

• Slide Controls  There are two slide controls to the right of the square buttons.  Predictably, the "Volume" slide allows you to fix the playback volume of signal.  Note that the volume of your Mac's speakers (and headphone jack) is ultimately governed by the Sound Control Panel.

The "Balance" slide lets you set the left/right balance of the signal, and ranges from left channel only (extreme left) to right channel only (extreme right).  To split the signal equally between the left and right channels, move this slider to the middle. In some cases (AudioVision monitors or when the Force Mono option is enabled, for instance), the balance control has no effect.

• Memory Buttons  At the bottom of the Digital Equalizer window is a row of five memory buttons which can be used to save and recall equalizer graphs.  To recall a graph, that is, to move it from memory to the Big Graph, just click its memory button.  To save the current state of the Big Graph to one of the memory buttons, hold down the option key and click a button.

(3) Other Features

• AutoLaunch  Available from the File menu, this feature allows registered users to have a CD player (or other program) automatically opened when they start up Digital Equalizer.

To use this feature, check the "AutoLaunch Active" box and, if necessary, select an application by clicking the "Select AutoLaunch Application…" button.  If you check "Keep Equalizer As Front Application," the equalizer will remain the frontmost application and the selected application will start up in the background.  If you don't check it, Digital Equalizer will start up and then immediately switch to the AutoLaunch application.

IMPORTANT-  Changes made to the AutoLaunch feature will not take effect until the next time you launch Digital Equalizer.

• Audio Preferences  There are three audio options, which you can set by selecting Audio Prefs… from the Equalizer menu:
     - Force Mono Play
     - Swap Left And Right Channels  
     - Enable Automatic Gain Control (some Macintoshes)

• Curve Preferences  There are three curve options, which you can set by selecting Curve Prefs… from the Equalizer menu:
     - Use More Pegs  Check this box if you'd like more pegs to shape the curve.
     - Horizontal Axis: Frequency  There are two available scales: equispaced octives
        and equispaced frequencies.  Select the former if you want fine control over
        low frequencies.  If you use the equispaced octive scale (the default), avoid
        steep bends in the left part of the curve (see Section 10).
     - Vertical Axis: Signal Strength  There are also two scales for signal strength:
        percent and dB (decibels).  Using the percent scale (the default) is probably
        the best way to go unless you have a specific reason to use the other.

• Colors  You can set the colors of the curve and its background from the Equalizer menu.

• Curve Save and Recall  You can save and recall equalizer curves from the Equalizer menu.  Alternatively, you can use the Memory Buttons (described above in "The Controls") to do the same thing.

(4) Quickstart Examples

IMPORTANT- Applies To All Examples: Digital Equalizer always plays audio through the default audio output device.  Unless you've purchased additional sound hardware, your Macintosh only has one, built-in, output device (which is the default, by default, so to speak).  The built-in output device plays sound through both the internal speaker and the sound-out jack at the back of your Macintosh.  If you're using an AudioVision monitor (speakers attached), the audio is also played through the monitor's speakers and sound-out jack.

You can adjust the volume of each output separately, from the Sound Manager Control Panel (choose "Volumes" from the pop-up menu).  This lets you handle cases when you want Digital Equalizer's sound to come through some outputs and not others.  For example, if you're listening through headphones plugged into the sound-out jack, you may wish to kill the volume of the internal speaker.  If you have an AudioVision monitor, there may be a total of four separate volumes to juggle.

• To use Digital Equalizer to listen to audio CDs played in the internal CD drive:

      1) Launch the Digital Equalizer application.
      2) In the Digital Equalizer window, use the Input Source button to select the
          internal CD. Successive clicks toggle between "Internal CD" (CD icon),
          "Microphone" (mic icon), and "AV Connector" (connector icon).
      3) Start the flow of sound from the internal CD to the Mac's speakers by
          clicking on the Player button. Successive clicks toggle between "on" (green
          arrowhead) and "off" (green stripes). Note that "Player" in this context has
          nothing to do with playing tracks from the CD.
      4) Use the Filter button to activate filtering. Successive clicks toggle between
          "on" (wavy line) and "off" (flat line).
      5) Put an audio CD in the drive and launch your favorite CD Player- for
          example: CD Remote, or AppleCD Audio Player.
      6) Now, when you use your CD Player to play tracks, the sound will be
          "equalized" before it's played.  

• To use Digital Equalizer to listen to external audio sources:

      1) Launch the Digital Equalizer application.
      2) In the Digital Equalizer window, use the Input Source button to select the
          microphone. Successive clicks toggle between "Internal CD" (CD icon), 
          "Microphone" (mic icon), and "AV Connector" (connector icon).
      3) Connect the external audio source to the audio input jack on the back of
          your Macintosh. Most likely you'll need a male-male cable to make the link.
      4) Click the Player button, if necessary, to turn the equalizer's player on.  This
          starts the flow of sound from the external source to the Mac's speakers.
      5) If the sound comes out distorted, lower the volume of the external source.
      6) Use the Filter button to activate filtering. Successive clicks toggle between
          "on" (wavy line) and "off" (flat line).

(5) System Requirements

• Any Power Macintosh  68K Macs just can't handle the heavy number crunching required for real-time filtering.  Additionally, most 68K machines lack hardware support for playing and recording CD-quality audio.  But, Digital Equalizer runs fine on even the slowest Power Macs.

• Sound Manager 3.0 or higher  This is available as an extension for Mac's running System 7.0 and 7.1.  In System 7.5, Sound Manager 3.0 is built in to the system software, so you don't need the extension. As of this distribution, Sound Manager 3.1 is the latest version.  If you're still running 3.0, I recommend that you install 3.1; it will greatly lighten the equalizer's load on the processor. The latest version of the Sound Manager is available free from most big online services- AOL, EWorld, Compuserve, etc., or via FTP from ftp.info.apple.com in the /Apple.Support.Area/Apple.Software.Updates/US/Macintosh/System/Other_System directory, filename: Sound_Manager_3.1.sea.hqx

(6) About Possible Sluggishness

Be aware that when Digital Equalizer is running on your computer, even in the background, it may lean heavily on the microprocesser.  This is not harmful to the system in any way; it just means that other programs running concurrently may act a bit sluggish.  This is an unavoidable consequence of the filtering algorithm, which literally performs millions of calculations per second.  However, this effect is not too untoward on my comparatively torpid 6100/60, and is no doubt less noticeable on the newer, faster PPC models.  As mentioned in the previous section, one way to mitigate this problem is to install Sound Manager 3.1 if you're currently running 3.0.

(7) Registering

To register, please send $15 (US only) check, cash, money order to:

Huben Consulting Inc.
6929 Lee Crest Drive
West Bloomfield, MI
48322

Please make checks out to "Huben Consulting Inc."  Within a week or two you'll receive a registration certificate containing an ID and password which you can use to register your copy (and all future updates) of Digital Equalizer.

Once you've registered your copy, shareware notices will no longer appear when you launch the application, and the About… box dialog will display your name next to the words, "Registered To:"  Also, the AutoLaunch feature will be enabled, allowing you to start your CD player (or other application) automatically just by launching Digital Equalizer.

A facility for printing an order form can be accessed from within the Digital Equalizer application by clicking the "Register…" button on the splash screen that comes up right after launch.

I've poured several hundred hours into this project, betting that Mac users will appreciate a unique, high quality piece of Shareware and make it worth my while.  So if you like Digital Equalizer, register it.  Your support will enable me to bring out other cool Shareware apps.

(8) Updates

I'll release updates to the major Mac shareware archives and electronic services (America Online, Compuserve, info-mac, etc...) as time permits.  The amount of shareware response will be an important factor in my decision whether or not to expand Digital Equalizer.  Accordingly, this version (2.0) may be the last one for a while.

Registered users will find that their password works on all future versions of Digital Equalizer.  Once you register, you're registered for good.

(9) Distribution

You may freely distribute the unregistered version of this program, provided that it has not been modified in any way and is accompanied by this documentation file.  If you want to include Digital Equalizer on a CD-ROM Shareware collection, however, you must send a free copy of the disc to Huben Consulting, at the above postal address.

(10) Known Conflicts / Problems

• Steep Curve Distortion  Sharp bends in the equalizer curve can sometimes result in distortion.  If you are using the equispaced octive scale, especially, avoid abrupt twists in the left half of the curve.

• Performa 6200/6220  The configuration of the sound input hardware in these models is unusual.  The internal sound input device is not capable of recording stereo, CD-quality audio.  And so, Digital Equalizer won't run on these machines.  However, some or all of these models have an Apple TV/video input card that does capture stereo signals.  I will try to get Digital Equalizer working with this card in the near future.

• The Global Village conflict has been resolved.

(11) Comments / Suggestions / Bug Reports

If you have any bug reports, comments, or suggestions, please send them to me at the above postal address (Carl Huben, C/O), or via email: CarlHuben@aol.com

(12) Disclaimer

Huben Consulting Inc., is not responsible for any operating system crashes, their repercussions (data loss, etc.), or any other problems resulting from the use of the Digital Equalizer application.

(13) Thanks

Thanks to the original beta testers: John J. Calande, Ed Klemz, Craig Marciniak, Craig Portman, and Judd Stiff.  Special thanks to Rustle Laidman, for tons of good advice and support.  

I owe a large debt of gratitude to the indefatigable and eagle-eyed tester, Heather Boyle.  Also, thanks to Jonathan Edwards for zeroing in on the Global Village Toolbox conflict, and to George Hazelwood for providing confirmatory info.  And I really appreciate Gary Chang's help in trying to understand the sound-input quirks of the Performa 6200 and 6220.

I'm grateful to Michael Brundage for his help in resolving the Global Village dilemma.

And, of course, thanks in advance to everyone who registers.

(14) Mathematical Notes

Q. What's going on with the first "seventh" of the equispaced octave scale?
A. Good question.  From 350 to 22 kHz (or 175 to 11 kHz with 22 kHz sampling), the graph is logarithmic in frequency.  But the portion between 0 and 350 Hz is linear.  The equalizer's algorithm doesn't permit fine control over this low frequency range.  There are two reasons for this: finite CPU power and the constraint that sound must be processed nearly in real time.

Q. Which decibels are you using for the scale?
A. Voltage decibels (not power decibels).  Therefore, the lower limit of -30 dB corresponds to about 3% of the original amplitude (not .1%).

(15) History

Version 1.0.0 released 10.7.95

Version 1.1.0 released 10.19.95
  - Lowered price to $15.  The original price was out of line with other shareware apps of commensurate value.
  - Added another audio buffer and fixed a delay duration constant to ensure that the recording won't get ahead of signal processing.
  - Fixed a bug which caused the "instant quit" syndrome when the recorder outpaced the signal processing; if this ever happens (and it shouldn't, due to the other fix, above) there will be an unsightly click instead.  This is good news, also, because now the user's pre-launch sound settings are never clobbered.
  - Fixed a potential crash bug in the preferences read routine, involving res file switching.
  - Added prefs dialog plus code to handle 3 new options: force mono, swap left and right, enable auto gain.
  - Added single sweep curve tracing with double clicks in big graph.
  - Expanded equalizer menu to include memory button saves & recalls.
  - Moved PPC assembly routines from precompiled libs to inline code, changed a few opcodes to ensure compatibility with new 60X flavors.
  - Added code to sweep out convolution work area each time the player starts up, not just the first time (smoother-sounding restarts).
  - More careful when setting/resetting optional input device selectors (playthrough, vox and others). 
  - Another input device selector (siActiveChannels, optional) is used to ensure that both channels of a stereo signal are digitized (fixes left/right drop-outs that occured on some Mac models).
  - Another input device selector (siInputGain/siStereoInputGain, optional) is used to ensure 0dB recording gain while program is running.
  - Dozens of assorted tiny bug fixes.
  - Improved error handling, plus much more error checking.

Version 1.2.0 released 11.19.95
  - Fixed the Global Village conflict.  For some reason, their software causes a crash when DEQ opens a window after a call to SndSoundManagerVersion.  I don't know why this is, but I've worked around it.
  - Added an AutoLaunch feature so that registered owners can have their CD player automatically opened when Digital Equalizer starts up.
  - It now correctly saves the position of the main window.
  - A few other bug fixes and cosmetic touch-ups.

Version 2.0.0 released 11.24.95
  - Added the Curve Prefs dialog, which allows for more pegs and log scales on both axes.  Having a log frequency scale is pretty important, which is why I released this new version so soon after 1.2.
  - All dialogs work correctly in the presence of screensavers.
  - Fixed a tiny asymmetry in the filter function.