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Most of us agree that the aim of good hi-fi is to re-create the sounds heard in the control room of the studio when the final mix of a piece of music is laid down onto tape or disk.  You just take a stack of the best high-end equipment and connect it up with the finest and eye-wateringly expensive cables and the end result will be a sound that will be within a flea’s whisker of the original. Surely the CD is a bit-to-bit exact copy of the original recording and the rest of the equipment, as the magazine reviewers never tire of telling us, is as close to perfection as makes no difference. As it happens, Stan Curtis spent some time in the studio recently re-mastering an old album for re-release and discovered again that the sound was head and shoulders above that from all other sources.

This is just one of the paradoxes Mr. Curtis set out to explore in his column, and again he provides us with much food for thought.

When the small "bookshelf" loudspeakers became popular some 30 - 40 years ago, they established a new market niche. Stereo setups could now much more easily find their way into normal living rooms. Many of these small speakers did not impress with their sound quality, however, although there were exceptions. On the other hand, most small boxes were aimed at a consumer market where the requirements on sound quality were low, if any at all. However, many small studio monitors, for example, meet very high standards on several parameters.

Lennart Jarlevang was approached by the owner of a mid-prized high fidelity loudspeaker of small size (net volume about six liters). The owner liked the basic tone and performance of the speaker very much, but complained about an annoying chill and harshness in the high frequency area. Initially thinking that this, as often is the case, was a tweeter issue, Lennart soon found the problem to be caused by a more interesting phenomenon. He set out to unravel the riddle and to modify the design for even better performance.

The development of artificial reverberation in the audio industry has been aimed at duplicating the sound of real rooms, more and more accurately.  No one ever considered the possibility of developing reverberation more desirable than real. Richard Burwen discovered that your ears really like to hear the high frequencies missing in room reflections above 5 kHz.  Their most important characteristic is not the spatial and echo effect, but thousands of peaks and valleys in the frequency response that tend to ‘clean up’ high frequencies in the music. Signal processing to achieve a wiggly frequency response having a carefully tuned trend can greatly extend the potential of an audio system and program material for realistic reproduction. This article discusses the thinking behind the system and explains the various processing options. Example sound files with different processing are available on-line at http://www.burwenbobcat.com .

A low-noise preamplifier with variable-frequency tone controls Vol 5

In 1996, Douglas Self published a design for what became known as the Precision Preamplifier, which included a treble/bass tone control with variable turnover frequencies. Starting with the idea to revisit the design with the benefit of years-long experience and newer parts, the design developed into much more than ‘just’ a tone control preamp. The necessary additional stage to correct the phase reversal of the tone control stage was called up for a Baxandall-type active volume control duty.

Then, reminding himself that we don’t all use symmetrical listening spaces, Douglas realized that a ‘vernier’ balance control would be very useful – but of course without interfering with either the tone or the volume controls. Add to that the need to maintain very low noise and distortion levels, and you have a article that is more like a tutorial on preamplifier design.