Traditional Analog to Digital conversion methods are based upon sampling of the original waveform. Therefore the sampling rate determines the quality of the reproduced sound. At 44.1Khz (44,100 samples a second), which is CD Quality sampling, the traditional sampling method still misses peaks and fast changes in a waveform that means certain frequency harmonics and intended noise gets lost on the conversion.

In the above graph the red dots represent what the reproduced waveform will look like. This is a known problem in the world of Analog to Digital conversion and is the reason behind the push to go to higher sampling rates, such as 96Khz (DVD Quality) and 192Khz (Production Quality). But as will be demonstrated soon, the biggest problem with these high sampling rates are the huge file sizes produced.

How often must we sample? The answer is actually known, and it's called the Nyquist Sampling Theorem (first articulated by Nyquist and later proven by Shannon). Roughly, the theorem says:

Sample twice as often as the highest frequency you want to capture.

For example, since the highest sound frequency that most people can hear is about 20 KHz (20,000 cycles per second), with some sharp ears able to hear up to 22 KHz, we can capture music by sampling at 44 KHz (44,000 times per second). That's how fast music is sampled for CD-quality music.

As to the vertical axis, CD-quality music uses 16-bit numbers for the vertical axis (i.e., bit-resolution=16), giving us 2¹⁶=65,536 distinct levels from lowest to highest. Using this, we can actually calculate the file size.

file size (in bits) = bit-resolution * sampling rate * recording time

For example, how many bits is 1 second of monophonic CD music?

16 bits per sample * 44000 samples per second * 1 second = 704,000
Therefore, 704,000 / 8 bits per byte = 88,000 bytes = 86 KB
 

That's 86 KB for one second of music! (Note that there are 1024 bytes in 1KB, so 88000/1024 is approximately 86KB.) And that's not even stereo music. To get stereo, you have to add another 86KB for the second channel for a total of 172KB. An hour of CD-quality stereo music would be 620 MB, or about the size of a CD!

In fact, it is not accidental that a CD can hold about 1 hour of music, it was designed that way. But the web bandwidth cannot compete with the playback speed of a CD. Think of how long it would take for that to be downloaded over a slow modem! Then again, the CD quality conversion methods have failed to deliver the kind of sound intended by musicians (per the example given above) so the music industry has pushed to go to higher bit rates, like 96Khz (DVD) and 192Khz (Studio Production) making the file size problem even bigger.

In the next screen, we will explain how WaveTrace can reproduce the wave perfectly without sampling the original wave and using smaller file sizes than CD quality sampling!