Sample, sample rate, sample format, and bit rate
The main function of the audio interface is to convert the signal between analog and digital formats.
As mentioned above, real sounds have endless possibilities for pitch, volume, and duration. Computers cannot process infinite information, so audio signals must be converted before they can be used.
Computer approximated waveform
Source: pcm.svg http://commons.wikimedia.org/wiki/File:Pcm.svg Retrieved from.
Figure 1.1 Computer approximated waveform
The figure in Figure 1.1, “Computer approximated waveforms” illustrates the situation. The red waveform shows the sound waves produced by the singer or acoustic instrument. The computer cannot handle the gradual change of the red waves. The computer should use the approximation shown in the gray shaded area of the figure. This figure is an exaggerated example and does not represent the actual recording.
Converting between analog and digital signals reveals the difference between low-quality and high-quality audio interfaces. The sample rate and sample format control the amount of audio information stored by the computer. The more information that is stored, the better the audio interface can approximate the original microphone signal. The possible sample rates and sample formats determine only a part of the quality of the sound produced or obtained by the audio interface. For example, an audio interface built into the motherboard can support 24-bit sample formats and 192 kHz sample rates. On the other hand, a professional-grade FireWire-connected audio interface with a 16-bit sample format and 44.1 kHz sample rate may sound better.
1.3.1. Shows
A sample is a unit of audio data. The computer stores video data as a series of still images (each called a “frame”) and displays them one at a time at a specified speed (called a “frame rate”). The computer stores audio data as a series of still sound images (each called a “sample”) and plays them back one at a time at a specified frequency (called a “sample rate”).
There are not many types of frame formats and frame rates that are used to store video data. There are many types of sample formats and sample rates that are used to store audio data.
