- Not to be confused with Computer speakers.
A PC speaker is a loudspeaker built into most IBM PC compatible computers. The first IBM Personal Computer, model 5150, employed a standard 2.25Â inch magnetic driven (dynamic) speaker. More recent computers use a piezoelectric speaker instead. The speaker allows software and firmware to provide auditory feedback to a user, such as to report a hardware fault. A PC speaker generates waveforms using the programmable interval timer.
Usage
BIOS error codes
The PC speaker is used during power-on self-test (POST) sequence to indicate errors during the boot process. Since it is active before the graphics card, it can be used to communicate "beep codes" related to problems that prevent the much more complex initialization of the graphics card to take place. For example, the Video BIOS usually cannot activate a graphics card unless working RAM is present in the system, while beeping the speaker is doable with just ROM and the CPU registers. Usually, different error codes will be signaled by specific beeping patterns, such as e.g. "one beep; pause; three beeps; pause; repeat". These patterns are specific to the BIOS manufacturer and are usually documented in the technical manual of the motherboard.
Games
The PC speaker was often used in very innovative ways to create the impression of polyphonic music or sound effects within computer games of its era, such as the LucasArts series of adventure games from the mid-1990s, using swift arpeggios. Several games such as Space Hulk and Pinball Fantasies were noted for their elaborate sound effects; Space Hulk in particular even had full speech.
Other programs
Several programs, including MP (Module Player, 1989), ScreamTracker, Fast Tracker, Impulse Tracker, and even device drivers for Linux and Microsoft Windows, could play pulse-code modulation (PCM) sound through the PC speaker using special techniques explained later in this article.
Modern Microsoft Windows systems have PC speaker support as a separate device with special capabilities â€" that is, it cannot be configured as a normal audio output device. Some software uses this special sound channel to produce sounds. For example, Skype can use it as a reserve calling signal device for the case where the primary audio output device cannot be heard (for example because the volume is set to the minimum level or the amplifier is turned off).
Pinouts
In some applications, the PC speaker is affixed directly to the computer's motherboard; in others, including the first IBM Personal Computer, the speaker is attached by wire to a connector on the motherboard. Some PC cases come with a PC speaker preinstalled. A wired PC speaker connector may have a two-, three-, or four-pin configuration, and either two or three wires. The female connector of the speaker connects to pin headers on the motherboard, which are sometimes labeled SPEAKER or SPKR.
Pulse-width modulation
The PC speaker is normally meant to reproduce a square wave via only 2 levels of output (the speaker is driven by only two voltage levels, typically 0 V and 5 V). However, by carefully timing a short pulse (i.e. going from one output level to the other and then back to the first), and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.), the end result corresponds to intermediate sound levels. This effectively allows the speaker to function as a crude 6 bit DAC, thereby enabling approximate playback of PCM audio. This technique is called pulse-width modulation (PWM) and is notably used in class D audio amplifiers.
With the PC speaker, this method achieves limited quality playback; the quality depends on a trade-off between the PWM carrier frequency (effective sample rate) and the number of output levels (effective bitrate). The clock rate of the PC's programmable interval timer which drives the speaker is fixed at 1,193.18Â kHz. This relatively low modulation frequency limits the resolution and produces poor but recognizable audio.
This use of the PC speaker for complex audio output became less common with the introduction of the Sound Blaster and other sound cards.
See also
- Intel 8253
- RealSound
- Loudspeaker enclosure
Notes
External links
- Smacky Open-source C++ software for playing songs on the PC speaker.
- Site for old PC without sound cards.
- PCGPE article on programming the PC Speaker.
- Part 1 of another article about programming the PC speaker.
- Part 2 of the article
(includes a very detailed explanation of how to play back PCM audio on the PC speaker, and why it works) - Bleeper Music Maker A freeware to use the PC speaker to make music (superseded by BaWaMI)
- Article about programming PC speaker using C++
- Commandline PC speaker program for LinuxFTP
- Practical article on implementing a Linux Kernel Driver
- Timing on the PC family under DOS (Sections 7.5, 7.29, 7.30, and 10.7 â€" 10.7.4 in particular)
