Hardware Reference
In-Depth Information
Introducing Audio
Science i ction i lms from the 1980s were full of strange machines with lots of
l ashing lights and annoying beeps. The i rst PCs sold had only a buzzer, and
the i rst versions could only do that, buzz. A while later, people played with
the buzzer, making tones and even music for games. There are various videos
on YouTube that show what games used to be like. Don't laugh; we really did
play like that, and we liked it!
The gaming industry was driving sound development at the time, and gam-
ers wanted more advanced music. It wasn't long before MIDI sound cards
were released. MIDI is a protocol for connecting musical devices together. (A
computer can also be a musical instrument.) Some sound cards could be pro-
grammed with “instruments” to be played back at different notes. Although
the sound i delity was much better than the original internal buzzers, it could
still be better. Music was certainly much better, but recorded sounds still were
not possible—or at least, not easily. You could listen to high-quality music, but
the explosions created by your rocket launcher wouldn't sound quite right. The
industry turned to another solution.
A new generation of sound cards was born: Creative Lab's Sound Blaster series.
It had the features of MIDI sound cards but also had digital signal processors
(DSP for short) that could create complex digital audio signals. Computer pro-
cessors were more and more powerful, and i nally powerful enough to create
complex sounds by digitally interpreting an analog signal through the sound
card. We could hear music, and explosions sounded great. We stayed up all
night hurling rockets at each other.
Again, new technology had its benei ts but also had a problem: space. Digital
sound i les took up a lot of space, and space wasn't readily available at the time.
High-end hard drives were just more than 1 gigabyte in size, and a 3-minute song
recorded from the radio could be hundreds of megabytes in size. If music were
to become digital, we needed larger hard drives or to i nd a way to compress
music, preferably both. Today, a song can be compressed into 4 or 5 megabytes
and placed onto a music player with gigabytes of space. However, it also requires
something else: faster processors.
Digital Sound Files
One of the i rst digital audio formats is known as wave : an uncompressed digital
i le that represents an analog signal. Where analog signals can have almost every
value possible between their maximum and minimum values, digital cannot. It
requires a resolution: the amount of values it can handle. On a scale of 0 to 10,
an analog signal would create a 7.42, but a digital signal from 0 to 10 in steps of
1 would not; the closest it can do is 7, as shown in Figure 18-1.
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