Using Sounds

The Classic Mac OS, in common with other operating systems, employs sounds that can enhance the user’s experience. Although the author prefers his computer to remain silent, especially when things are going wrong, this can be helpful to some people, especially those with limited eyesight.

The most common sounds on a computer are:-

Alert Sounds

This kind of sound is usually heard when an error occurs, although the same sound is often used to indicate that a job has been successfully completed.

Startup Sounds

Most computers generate a sound during the startup process, usually indicating that the machine’s hardware tests have been completed. In some computers this sound can’t be disabled, although you can push a dummy plug into the sound output socket to turn off the sound output. Unfortunately, this also prevents any other sounds from being heard.

  The Sound Control Panel

The Classic Mac OS contains a Sound control panel for adjusting the sound settings. This is divided into Alerts, Input, Output and Speakers sections, although the Main Volume control is always at the bottom of the window, allowing you to set the overall volume of sound.

The most significant sections in the panel are described below.

Alerts

This part of the panel is shown below, with Simple Beep chosen as the alert sound.

The Alert Volume control is useful, especially on modern machines that can generate alerts and other sounds simultaneously. For example, when using Text-To-Speech (TTS) the volume of a voice is set by the Main Volume control while the alerts are also influenced by the Alert Volume setting.

If you select New Sound you’ll see the following window:-

The function buttons and elapsed seconds counter work in a similar way to those on a real tape recorder. When the recording is complete you can click on Save to store the result.

Input

This part of the panel lets you select one of the available sound input devices, as shown below:-

The most common options are as follows:-

SourceDescription
Built-in MicIntegral microphone, as fitted in a PowerBook
Expansion Bay •PowerBook bay, usually containing a CD-ROM drive
External MicMicrophone connected via sound input socket
Sound InSound input socket
Suitable for recording part of an audio CD track - use a utility to import an entire track

Output

This section of the panel appears as follows:-

Unless your machine has extra audio hardware, the list will only show Built-in, meaning that any sound that your machine makes will go to its sound output socket.

System and Application Sounds

  Appearance Control Panel

This control panel lets you use a particular theme for your computer desktop. It can also make your computer produce a special range of sounds, each one associated with a particular action. These sounds can be enabled by clicking on the Sound tab and choosing a particular set of sounds from the Sound track pop-up menu, as shown below:-

In this case, Apple’s default Platinum Sounds are selected, although other sets can be used.

  SimpleSound

This application, supplied with the Mac OS, can create alert sounds in a similar way to the Sound panel. In addition, it can open sound files that aren’t inside the System file. When you do this, a window appears, showing you the file’s resolution, whether its mono or stereo, its sample rate and duration. To hear the actual sound just double-click in the window.

SimpleSound introduces a slight complication regarding the formats of sound files. The traditional alert sound, as found in the System file, is identified as a sound by the Finder, has a dog-ear on the left-hand side of its file icon and can be heard by double-clicking on the file. However, a SimpleSound document is entirely different, with the dog-ear on the right-hand side. This modern AIFF-C sound file can only be opened in SimpleSound or with the assistance of another sound application.

  Sounds in SimpleText

SimpleText, the basic text editor supplied with the Classic Mac OS, can also record sounds and automatically save them in the current text file. To make a recording, select Record in the Sound menu and the standard recording window appears. Once your recording is complete you can recall it by selecting Play. To get rid of the recording, simply select Erase.

  Classic Mac OS Sound Resources

The Classic Mac OS can use the resource fork of a file, such as that belonging to an application or other software, to store sounds. These are normally kept as a sound resource, which is identified by a code of snd<space>, where <space> is a space character. This kind of resource was introduced at the time of the Mac II computer and can also be found in documents recognised by the Finder as sound files.

Sound Resource Types

Standard Classic Mac OS sound resources come in two kinds:-

Format 1

Also known as a normal resource, this kind of resource contains instructions for the system’s Sound Manager. It can be used to store any combination of sounds, including sound samples or synthesised material that’s been created using frequency-modulation (FM) or wave tables.

Format 2

Originally designed for use with the HyperCard application, this kind of resource can only contain a sound sample. This format is obsolete and may sound incorrect, especially with 16-bit stereo sounds.

Sound Resources in Detail

The way data is stored in a sound resource depends on the type of sound sample. 8-bit samples are kept as unsigned bytes, as in the data fork of an older FSSD sound file, while 16-bit samples are signed in the same way as in a modern AIFF file. MACE 3:1 or 6:1 compression is optional.

In some applications you can edit the header within a sound resource. By modifying this information you can modify the playback sample rate, although the actual sound data remains unchanged. The structure of the header depends on the sound sample itself, as shown by the following table:-

Header TypeSampleFormatCompression
Standard8-bitMonoNo
Extended8-bitStereoNo
Extended16-bitMono or stereoNo
Compressed8/16-bitMono or stereoYes

©Ray White 2004.