High Fidelity

When I built my Williamson Amplifier and loudspeaker that weighed about a ton, in the mid 50s, the definition of High Fidelity was to reproduce the sound to be a faithful representation of the original source, to the extent that the "equipment" would be totally "transparent" between the input (microphone) and the output (loudspeaker). Thus no forms of distortion or colouration of the sound was permitted. The technology of the transistor was in it's infancy so all developments were using valve technology. And it was difficult to engineer an amplifier that could deliver much more that about 10 watts of power. So it was imperative that loudspeakers had maximum efficiency. (These days amplifiers can deliver hundreds of watts that loudspeakers need not be at all efficient and are typically only about 10%). Storage of the music on records or magnetic tape was in the natural analogue state.



The Williamson amplifier was the first serious attempt to meet the needs for the domestic environment. Although it excelled, the system still would rely on the integrity of the "weak" links, namely the Radio, record player (tape recorders at that time had not ingressed into the home) and of course the Loudspeaker.

Only one was needed because the word "stereo" was not a considered concept. In those times, all the development was based on storage and transmission of analogue signals. The BBC was working on "frequency modulation" radio transmissions, and the micro groove vinyl record was being produced and continually improved. And in the amplifier domain, transistor analogue technology was being pursued.



The first major development, which was going to question the definition of Hi-Fi, was when the record engineers developed the micro groove holding two signals capable of being captured with the one record needle. Although the principles of stereo were well understood, it was this breakthrough that would change the whole domestic scene. In another chapter I discuss "projective correspondence" but suffice to mention here that stereo sound is an auditory illusion. This of course was a big commercial bonanza because our one amplifier and one loudspeaker were redundant. We now needed two of everything!



The next major change was digitising the signal for storage purposes, initially on magnetic tape but soon after, about 1980 when the compact disc first appeared.

It might not readily be appreciated but the moment an analogue signal is converted into binary digits, an enormous amount of information is lost and completely unrecoverable. And the question is "does it matter?" Well it doesn't seem to does it?. But to understand just why, it is worth looking at the history of the movie industry.

How the movies moved!

Although the early filmmakers probably did not understand the limitations of the human brain, they nevertheless took full advantage of our frailty.

Actually we cannot absorb too much information very quickly.

If any two events occur less than 80ms apart (0.0125 sec) we can only perceive one of them.
Also we can only absorb 40 (binary) bits per second.

Now a movie film is a series of still photographs which are "gated" through a projector. And the first standard projectors operated at 16 frames per second (fps). However, we were presented with a moving picture having annoying flicker, because 16 fps was uncomfortably close to our perceptual limit of 13 fps. But the 16fps nevertheless carried all the information our brains could handle, so there was no need to increase the fps which would add significantly to the bulk of the spool of cine film. The clever trick the industry found worked wonders was to simply gate each frame 3 times. So while a frame was in the gate, a shutter would pass over two more times before moving onto the next frame.

This was the equivanlent of 48 fps and the flicker was completely removed, resulting in the perfect moving picture.



Taking a movie picture is no different from taking a normal camera photo except 16 are taken every second. A typical exposure time might be 2ms (1/500 sec). Then there is another 60ms before the next picture is taken. So we see that what looks to be a perfect moving picture, has nevertheless thrown away something like 96% of the available information!

Because of the limitation of our brain, we are not in the slightest, aware so much data or information has been lost; unless, that is, it is brought to our attention.



For example, High-speed cameras that can film at say 1000 fps can track fast moving objects like a bullet trajectory. This is something we could never see in actuality and it is of scientific interest to view such a film in slow motion. That is at 16 fps. Such a film highlights the fact that so much information is "ditched" with normal filming. It is of course of academic interest, because our brains could not perceive the information if it had not been lost. We are totally unable to monitor the trajectory of a bullet.



About the time talkies started I believe in 1927, the industry standard changed to 24 fps with double gating so the equivanlent 48 fps remained the same. Although this increased the film bulk by 50%, it was done for the benefit of the optical audio track, which runs along the side of the 35mm film and was only changed for that reason.

And those industry standards, set up in the late twenties, have remained unaltered to this day.

Except that is for our Digital Cameras in movie mode. A cursory glance at the specification will show that in the interest of keeping the storage as small as possible, the frame rate can be significantly reduced, often as low as 15 frames per second. In this case the Camera's firmware looks after the sound and ensures there is no irritating flicker.

Although these film industry standards do not relate directly to digital technology, their standards demonstrate very well how a series of snapshots discard enormous quantities of information.

And that is exactly what digitised audio signals are. A series of snapshots. And just like the movies, we remain totally unaware that we are "missing" any information at all!




Film and sound differ in one important way. In movies, our eyes are presented with the information at the equivalent of 48 frames per seconds and our brain in effect does the smoothing. In the case of digitised audio, the data is converted back to an analogue signal before presenting to our ears. The process of digitising and converting back again to analogue, can introduce a form of distortion called "quantisation distortion". And our CD player's firmware has to work very hard to ensure this distortion is kept as small as possible.

And it is in this respect along with the fact that data is irretrievably lost between digital samples, that devotees of the old vinyl records consider the CD reproduction is poorer.


If you would like more information on this form of distortion, you will find a visit to Quantization Error curtesy of Wikipedia, will be an informative site.


But a word of warning.

These days the salesmen and media will have us believe that "digital" is synonymous with "high fidelity".
TOTALLY WRONG. Digitalised data can never be better than the analogue material from which it was derived. And at best, it will be no worse.


In making this sweeping statement, I am the beneficiary of "remastered" audio and video material. Especially early jazz and early movies. In my book, the best thing since sliced bread! And surround sound for me can be and often is, so realistic that it fits perfectly to the original definition of high fidelity.


Far from knocking it, I am a supporter of digital technology. Which is so good, there really is no need to sell the idea on a lie.

TO BE CONTINUED