Jim's Audio Pages and Websites

I have produced a variety of webpages and websites on audio-related topics. Some are on my personal website, other - more technical - ones are on my University website. The following is a set of brief descriptions of these pages/sites with links you can follow if interested.

Scots Guide to Electronics. This is the main website I have produced, and has a large number of pages on all sorts of areas of electronics.
Audio and Analog. This is a section of the Scots Guide with is specifically devoted to the areas of electronics and physics relevant to analog audio. Topics covered include the properties of cables and an analysis of ‘skin effect’. The pages also consider things like ‘bi-wiring’ between amplifiers and loudspeakers.
Armstrong Audio. This was a UK company who produced radio, audio, and hi-fi equipment from the late 1930's until the early 1980's. I worked for them for a few years so have produced a fairly extensive set of webpages giving information about them and their products.
J. E. Sugden Class A Power Amplifiers. In the 1960s Jim Sugden was the first to produce commercial designs for Class A solid state audio power amplifiers that were sold for use in domestic Hi Fi systems. These pages look at the early history of Jim Sugden’s designs and the details of the circuits he devised.

I occasionally produce one or two pages to deal with specific points that arise when I discuss audio equipment, or read articles in magazines or postings on newsgroups. The following lists a few examples of such issue-specific pages. First, some pages based on articles that first appeared in Hi Fi News magazine. The dates given are the cover-date of the issue of the magazine when the original version of the article was published. However many of the pages below contain extra material which wasn't included in the magazine versions.

Good Resolutions. This consists of two pages based on an article I wrote comparing the noise and dynamic range properties of LP and CD-Audio. There is also an extra page, dealing with some misunderstandings and comments in two letters about the article which appeared in a later issue of Hi Fi News. (April 2005)
Sound on Vision. Having bought a Digital Terrestrial TV (DTTV) receiver I discovered that I often preferred the sound quality for BBC Radio 3 on DTTV to that on FM. I also found that I preferred the sound on BBC4 TV when they were ‘symulcasting’ something like a Prom concert. The page looks at some of the differences between DTTV and FM, and suggests possible reasons for the DTTV broadcasts being preferrable to FM. (March 2006)
Clipping on CD. Having compared the dynamics of the audio broadcasts used for UK digital TV and radio I decided to do a similar comparison of LPs with CDs. The results show clear signs that many pop and rock audio CDs are more level compressed than LPs, and are often also severely clipped! (December 2006)
Hearing and Audio. This is a collection of pages on how human hearing works and the implications that may have for audio equipment. These pages are based upon various articles in Hi Fi News and Living with Technology. (Various dates in 2004)
Out of Tune. This page compares the behaviours of Single-Ended (SE) and Push-Pull (PP) power amplifier arrangements to see if some of the claims made about SE arrangements stand up to scrutiny. In particular, the two are compared by using test waveforms which are rather more like music than a simple sinewave. The results show that the SE arrangement can produce significantly greater anharmonic distortion than PP in such cases. (January 2007)
SCAMP -The Society for Cruelty to Amplifiers. This page explains the surprising demands that some loudspeakers impose on the power amplifier without the user knowing. In practice, the loudspeaker designer creates a problem which the amplifier designer then has to solve. The page calls upon audiophiles of the world to rebel against the reactionary loudspeaker designers! (April 2007)
Bandwidth Blues. This page investigates the levels of distortion which are inherent in real-world FM audio broadcasts as a result of the transmissions having to be confined to a limited transmission bandwidth. The effect means higher distortion levels than you might expect from the measurements published in reviews - even when you use a superb tuner and antenna system! (July 2007)
Over The Top! This page examines a problem which can arise when a waveform has excursions in between samples that exceed any of the sampled values. This effect is particularly important for digital recordings or broadcasts which have been made as loud as possible. As a result, a player may have to output signal levels from 1dB to more than 5 dB greater than the nominal maximum 0dBFS level. At the time of writing it is not clear how many (if any!) CD players can cope with such high levels. Since many rock and pop CDs are clipped and excessively loud, the result may be signal distortions which vary from player to player and disc to disc. (August 2007)
It was 40 years ago today... This page is a web version of an article looking at the early work of J. E. Sugden on Class A power amplifiers, and the role which Hi Fi News played in that process. If you want to know more about the early Sugden designs then also try the link near the top of this page. (June 2007)
Radford Revisited. This page looks at the work by Arthur Radford and Arthur Bailey developing outstanding valve power amplifier designs in the early 1960s. The page also provides a link to circuit diagrams, etc, of the early designs. (September 2007)
Keep in Contact. This page examines the various physical effects that impose limitations on the maximum signal level which can be recorded onto, and replayed from, a 33rpm Vinyl LP. It also assesses the demands placed upon the stylus design to be able to stay in contact with the groove walls! (January 2008)
On The Record. This article is a companion to the ‘Keep in Contact’ one and provides some real-world results to compare with the limits predicted from basic physics and engineering. It shows the results of measurements on the peak velocities and accelerations found on a variety of LPs. I didn’t have space for all the results in the magazine article. So I have provided an extra Gallery page showing the results I left out of the magazine. (February 2008)

Now a variety of other audio-related items...

Sales of CDs, LPs, etc. Comments and claims about the levels of sales of vinyl, etc, often appear in magazines and elsewhere. These usually only quote one or two figures taken out of context. I therefore decided to produce a webpage that gives the main figures for the UK and USA so people can decide for themselves what to make of them.
Bass performance of Quad FM4. This is an analysis I worte as a result of discussions about the FM4 tuner. Comments have been made to the effect that this “lack bass” so I decided to investigate...
Audio Formats. This is an article that was originally published in Living with Technology magazine. It gives a basic explanation of the Linear PCM (LPCM) form in which audio signals are stored on Audio Compact Discs (CD-As), etc.
Dolby Digital and DVD-Video audio. This is a follow-up article to the above, also originally published in Living with Technology magazine. In this article I give a simple explanation of how Dolby Digital works, and how this audio format differs from LPCM.
In a Dither. This is a set of pages that explain how ‘dither’ works. I wrote these pages after repeatedly seeing false or misleading statements in one UK audio magazine about the (alleged) performance limitations of CD audio. In particular, the pages show that it is simply wrong to claim that for correctly produced audio CD's, “The distortion rises for small signals below -60dB.” It also shows how audio CD (and digital systems in general) can record and reproduce low level signals.
Dirty Digital Delusions. This page was prompted by a specific magazine article which contained dubious claims about disortion and the CD Audio format.
Making sense of supertweeters. There has recently been a growing interest in “supertweeters” (sometimes called hypertweeters). These are loudspeaker units that are intended to extend the frequency range which a loudspeaker system can radiate. Typically, they are designed to cover the region above 20 kHz. This page outlines an argument which could allow a supertweeter to have an audible effect even if we can't hear the frequency range they are designed to cover!
QUAD 57 and 303. This page uses the combination of the QUAD 57 electrostatic loudspeaker and the QUAD 303 power amplifier to examine the changes in overall frequency response which can occur as a result of an interaction between the output impedance of an amplifier and the load impedance of a loudspeaker.
Apcable. Many manufacturers of exotic/expensive audio cables make technical claims for their cables and offer what appears to be ‘scientific’ justifications for their claims. This page considers a reasonably typical page produced by a manufacturer and carries out a critique of their technical claims. The example chosen was picked purely for the sake of an example. Nothing I write should be taken to imply the specific cable is any better or worse than any others. It is not a review or analysis of the cable as such, but of the technical statements made by the makers.
Asymmetry. Musical waveforms often show distinct asymmetries. This page shows some examples. This page was produced as a result of some discussions regarding the audibility of ‘phase’ and polarity in audio signals.
Amplifier distortion and waveform asymmetry. This is a set of three pages that consider the possible effects of the asymmetry of some musical waveforms upon the behaviour of power amplifiers. The pages also outline a test method that could be used to evaluate this area.
Turntables. The performance of some the turntable/arm/cartidge combinations used to play Vinyl LPs may be affected by system resonances and coherent acoustic feedback. This page shows examples of some measurements carried out around 20 years ago, and gives a brief consideration of why they may affect the sound.
Vinyl Solution. This page was produced as a result of a newsgroup discussion regarding the possible effects of clearing/processing LPs. The graphs are the result of analysing some soundfiles provided by someone marketing a specific solution.
Spikes and cones for loudspeakers. This page discusses the use of accessories like spikes and cones with loudspeakers. It was prompted by repeated comments in magazines that these ‘isolate’ the vibrational energy they produce.
Active filters for bi-amping arrangements. This is a couple of pages that go through how to design simple active filters for use as active crossover networks for use with bi-amping of loudspeakers. The filters are to ensure that each power amp and speaker unit only has to deal with the frequency range the speaker unit is designed to radiate. Note, though, that the explanation and analysis ignores many details which affect specific speaker units as these vary a great deal from one speaker to another.
Loudspeaker Cables. Questions often arise regarding what cables to choose for use with loudspeakers in an audio system. This page explains the role of resistance in this choice, and gives some examples of what type of cable may or may not be chosen.
Cable Sounds. Arguments about cables altering the ‘sound’ of an audio system regularly appear on the uk.rec.audio newsgroup (and elsewhere). This page summarises some of the comments I found I was repeatedly making on the newsgroups, and is designed as a reference for people from that group.
DAB Transmitters in Central/South Scotland. This simply shows the locations and powers of the DAB transmitters in the area around where I live.
Archive Articles. ‘Archive’ is a magazine for people who have an interest in using computers running the RISC OS operating system and its software. I have been writing a series of articles for the magazine. These deal with the use of sound data files. The articles therefore contain some explanations which may be of more general interest. They are accompanied by some example applications (programmes) which you are welcome to download and use. PLEASE NOTE that these applications only run under RISC OS. They won't work on a Windows box or a Mac unless you use a suitable emulator for a RISC OS machine!

The above articles include results I obtained by using computer programs I wrote for that purpose. The programs I write are all for the RISC OS operating system, and some of them are available via the Archive Magazine pages above.

You might like to visit Keith Howard’s Audio Signal website. In addition to a number of interesting articles, it provides some Windows executables for similar tasks. In particular, it now provides a Windows executable for analysing and plotting the statistics of the dynamics of sound files. This is called dynamicsanalysis and can be obtained via his freeware page. It can be used to obtain results similar to those in articles like the ones on Clipping on CD and Sound on Vision, above.

If you are also interested in non-audio topics, the main index page for my personal websites can be visited by clicking here.

Content and pages maintained by: Jim Lesurf (web@audiomisc.co.uk)
using HTMLEdit and TechWriter on a StrongARM powered RISCOS machine.