Transcript Sound & Computers

Adam Diel
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In 1981 IBM PC 150 introduced the first PC
Speaker.
Each game had to write support for it (sound cards
were impractical during this time)
 Could only play one square wave at a time
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It wasn’t until 1988 the first sound card came to
the market.
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Introduced by Creative Labs
Created ability to have multiple channels playing
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All sound that the human ear hears
is an analog signal
 A continuous electrical signal
In order for the computer to do
anything with it, it must be
digitized.
 Converted to 1’s and 0’s
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DAC = Digital to Analog Converter
ADC = Analog to Digital Converter
The soundcard of a computer (integrated into
the motherboard or an extra peripheral) will be
both the DAC and ADC for the computer.
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DAC for input (using a microphone for skype)
ADC for output (playing music on speakers)
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Sample Rate = The number of times
your audio is measured per second.
 The standard for CDs is 44.1 kHz
(44,100 slices/sec)
 The higher the sample rate the
better the quality
Audio is sampled at every
dash on the graph
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Bit Depth = Also known as the resolution of the
file, this is how many bits you have to capture
audio
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Think of it as a series of levels that audio can be
sliced into at any given moment in time.
Bit Rate = How much data per second is
required to transmit the file.
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How big the file actually is.
Usually used to measure quality in lossy formats.
Each Line Represents One
Bit of Data
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Dynamic Range = Largest amplitude the sound
file can contain without distortion.
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Think of this as the highest/lowest level on the
sound wave from the bit depth.
Dynamic Range
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Noise = Unwanted noise on an audio track
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Also known as white noise
Could be a number of things, bad shielding, poor
DAC or ADC, power supply, etc.
Without Noise
With Noise
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Distortion = alteration of the original shape (or
other characteristic) of a sound wave.

This could be done on purpose
 Electric Guitar Player’s have distortion pedals
 Special effects like echo’s
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Clipping = A form of distortion that occurs
when an amplifier/speaker is overdriven
WahWah
Clipping
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General misconception of “if it’s good enough
for CD it’s good enough for me.”
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Much of the audio quality is lost. People don’t
realize what they are missing.
Low
Medium
High
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Can be divided up into three categories
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Uncompressed
LossLess
Lossy formats
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These are WAV (windows) or AIFF (mac) files
that are considered ‘lossless’ files.
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Roughly 10MB per minute
The initial recording of sound is usually done
in this format before being compressed down.
CDs (not MP3 CDs) are uncompressed sound
files.
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It’s why you can only get 80 minutes vs 700 MB
(roughly 700 minutes of mp3)
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FLAC (Free Lossless Audio Codec), Apple
Lossless Audio Codec, and Monkey’s Audio
codec are all examples of this.
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Roughly 5MB/Minute
These are specifically designed for Audio files
and lets you convert back to uncompressed
formats.
These formats are ideal for the audiophile with
great sound setup.
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The most common formats used today, Mp3,
AAC, & WMA (Windows Media Audio)
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Roughly 1 MB/Minute.
Quality of these files can be referenced by the
bit rate of the file. The higher the bit rate, the
more that was preserved in the compression.
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Also means a larger file size.
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The reason why Lossy formats are so popular
is the amount of space uncompressed sound
files can take up versus compressed files.
Back when storage wasn’t as cheap this was a
huge benefit to home users.
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Has four basic components
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Analog-to-digital converter
Digital-to-analog converter
ISA, PCI, PCIe interface to connect to the
motherboard
 Unless integrated
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Input/Output Connections for microphones,
speakers, etc.
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The ADC will translate analog waves into
digital data.
The DAC will reverse the process of the ADC
to reproduce the original analog signal.
Rather then having separate ADCs and DACs,
soundcards will often integrate these into a
single chip called a CODEC
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1/8 Inch (Most Common)
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Optical
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The standard headphone jack
Can only handle two channels
Very small connection, digital connection
Coaxial SDPIF (Sony/Philips Digital Interface)
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Using the RCA connect, digital connection
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Two popular connects used in computers today
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AC’97 – Created by Intel in 1997
HD Audio – Also created by Intel in 2004
These are generally used for internal CD drives
Most modern motherboards have connects for
both.
HD Audio is able to support 32-bit sampling
resolution
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Most hardware manufactures don’t support this yet.