Follow Ups:Category: General Interest
From: klb (kate bullock)
To: ALL
Date Posted: April 10, 2005 at 09:45:44
Subject: Music technology desperate plea!
A plea to all techy whizzes...I am a lecturer at an FE college, currently teaching Digital Audio Principles to National Diploma Music Tech students.
I have not had a lot of experience in this area, so I have been gathering information from many sources in order to deliver it to my students.
I recently started on the subject of aliasing, and took my information from Hugh Robjohns' articles 'One Bit at a Time' published in the Sound on Sound magazine.
In one of the articles, he says that '...The sampling process chops up the analogue audio signal ready for quantisation, as discussed in this article. However, the process is actually a form of modulation where the audio signal modulates the amplitude of the individual samples. Any modulation process produces images of the original audio at the sum and difference frequencies -- in this case between the audio signal and the sampling rate -- and although these images are a side-effect of the process and serve no practical purpose, they do have significant implications.'
After quoting this information to my students, I ran into trouble - my fellow lecturer, with considerably more expertise than me in this field, disagreed with the information above. He, and many of his techy friends, cannot see HOW a SUM FREQUENCY can exist as a side effect of the sampling process. Consequently, he has contradicted the information I gave, making me look unreliable and untrustworthy. Being a perfectionist, this has caused me many sleepless nights.
I have tried to get in touch with Hugh Robjohns several times, but he is ignoring my pleas.
Is there ANYONE out there who can dispell this myth, and explain the sampling process...does Mr. Robjohns know what he's talking about? Should I ever trust him again? Does the SUM frequency exist?
That is my plea. I really hope someone out there is able to help me.
A very distressed lecturer.