Historically, the effectiveness of an audio system has been judged on the basis of how accurately the system reproduces the original event. Typically we might listen to a recording of a string quartet and compare it with our experience of what that ensemble sounds like in a live performance. The slogan "is it live or is it Memorex?" reinforces this traditional notion of fidelity in the consumer marketplace. Today's audio productions have seized on the vast creative resources in audio technology to create recordings which defy our sense of a recording faithfully reproducing a live performance.
Issues of Fidelity
In comparing the performance of audio systems these three factors should be taken into consideration:
Digital
Audio Recording
At the heart of hard-disk recording and editing is digital audio.When we record
digitally, sound is converted to an electrical signal by a microphone. That
signal is coded into numbers by an analog-to-digital converter (ADC). The numbers
are stored in memory, then played back upon demand by sending the numbers to
a digital-to-analog converter (DAC). The resulting signal is sent through an
amplifier and speakers so we hear a reproduction of the original sound. This
is illustrated by the animation below:
Devices used to capture, store and access sound will fall into some combination of the following categories:
Some examples:
Any type of audio recording system has 3 major components:
In digital recording we start with an analog audio signal and convert it to digital data to be stored. Changes in electrical voltage are encoded as discreet samples. On playback we retrieve the digital data and convert it back to an analog signal. Here, fidelity is dependent on the quality and function of the Analog-to-Digital (A-to-D) and the Digital-to-Analog (D-to-A) converter. Once an audio signal is stored as digital data, the storage media has no effect on the quality of sound.
The following chart shows storage requirements for a one-minute stereo audio file at different sample rates and resolutions. What is the tradeoff here in terms of fidelity vs storage? What is the frequency response for the different sample rates.
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Storage requirements for one minute of stereo digital audio.
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96k
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22
MB |
33
MB |
Storage requirements for one minute of stereo digital audio.
If you plan on doing any type of live recording with your laptop, the first thing you'll need is a microphone. As the first link in the audio chain, a microphone acts as a kind of measuring device which outputs a small, continuously varying AC voltage in response to the changes in atmospheric pressure caused by any sound disturbance.
Performance Characteristics
There any many makes and models of microphones, each with it's own set of characteristics. When evaluating different microphones, there are three important factors to consider:
These three factors are often integrated in a microphone's performance characteristics. When shopping for a microphone, look at these specifications, think about what the microphone will be used for, and choose accordingly. Manufacturers will often make suggestions on applications for their products, and trade publications, such as Electronic Musician, will often have articles and reviews.
Suggested Additional Reading: For a more detailed overview of microphones, read this article from the Electronic Musician archives: Building a Microphone Cabinet on Any Budget; Electronic Musician; September 2000.
ADC
Analog
Bit depth
DAC
Digital
Distortion
Frequency Response
Linear/Non-Linear
Nyquist Frequency
Random Access
Resolution
Sample Rate
Signal to Noise Ratio
Cardioid
Condenser microphone
Dynamic microphone
Omni-directional
Phantom power
Polar pattern
Proximity effect