Jim's Audio Pages and Websites

Time 2021-06-04 21:17:52

Web Name: Jim's Audio Pages and Websites

WebSite: http://www.audiomisc.co.uk

ID:181166

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I have produced a variety of webpages and websites on audio-related topics. This Audio Miscellany site concentrates on home audio. 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 has a large number of pages on all sorts of areas of electronics.Audio and Analog. This is a section 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 and the effects of clipping on 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.The following links are mostly to webpages related to feature articles and my monthly column in Hi Fi News magazine. Many of the pages contain extra material which wasn't included in the printed magazine.The dates given are the cover-dates of the relevant issue of the magazine.You can click on one of the above buttons to jump to the section for a specific year. Otherwise you can browse down this page. The items are arranged below to start with the newest additions to make them easier to find if you've visited before. The rest are then listed in chronological order. Mostly Quite 'armless . . .? A number of (nominally) Audio CDs have now been released which are MQA encoded . Streaming of this format has also begun. So events made me think it was time to re-evaluate the process and its potential impact. This page looks at one aspect of the issue. All being well, I'll look at other aspects later on.An Audio Test-Bench based on USB Audio devices and open-source software. This page shows how we can now use open source software and easily available USB Audio devices to make accurate measurements to examine and assess the performance of our home Hi Fi equipment. Useful to check that all is well and to optimise what we hear.BBC FM Stereo and NICAM3. The BBC's Stereo FM broadcasts are generally regarded as having a superior sound quality to the DAB radio alternatives. Given the modest bitrates and choice of codec for UK DAB this is an understandable reaction. However although Stereo FM broadcasting itself is an analogue system the BBC's transmitters are fed using the NICAM3 digital system they developed some decades ago. Given the progress since in digital codecs it seems reasonable to wonder if NICAM3 remains satisfactory, or if it significantly limits the sound quality. This page investigates this question...BBC FLAC Lack, alas... The BBC ran a test during the 2017 Proms where they provided an experimental live FLAC stream version of their Radio 3 output. Although you needed to find and use new software to access this, the resulting sound quality was superb. As a result, people eagerly anticipated that FLAC streaming would be resumed by the BBC for the 2018 Proms. Then - hopefully - it would become established as the new top-quality standard for their Radio output. But, alas, this didn't happen. I spoke to various people at the BBC about the issue and this page outlines what I found out, and gives my own views on the topic.Ringing on the line. Some recent discussions about the response behaviours of items like microphones and LP replay cartridges prompted me to have a fresh look at one aspect of the behaviour of the stylus systems used in cartridges. This shows the results of considering their mechanical behaviour in terms of applying transmission line theory. Master Quality Authenticated or Bit Freezing? This is a set of pages that examine the ideas and methods employed for MQA to try and squeeze higher audio quality into smaller files or data rates. One of the pages also outlines an example of an alternative method which is free and open . This alternative may avoid some of the side-effects of MQA while being able to fit high resolution data into smaller files or lower stream rates. This approach is one I have called bit freezing .Getting High Rez into shape. Thinking about other ways to reduce file or stream sizes using open and free methods it occurred to me that Noise Shaping could be employed for this purpose. This techique is widely used for other tasks. Indeed, it is already employed to make SACD/DSD a 'high resolution' format despite that only using one bit per sample! It occurred to me that the biggest bar to it being employed for high resoultion LPCM is that most people don't understand how it works or what it can do, and tend to mistakenly assume high rez must require more than 16 bits per sample. But that ain't necessarily so... 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)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)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)Like with Like?... This page is an expanded and updated version of an article that compared the dynamics and level compression on FM and DAB. The results show similar behaviour to the earlier comparison of FM and DTTV, but the article provides more details of the level compression behaviour. (April 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! (May 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)Around The Bend. This page carries on from the above and is the third in a series on the performance limits of Vinyl LP. It examines the groove curvatures and accelerations on LP and the implications for the tip mass and curvature required for a replay stylus (May 2008).New Lamps for Old. This page compares the measured performance of my old Shure V15/III cartridge with some new MM types. Results and stylus profile photos are shown for the V15/IIIMR, V15/IIIHE, Shure M97xE, Rega Exact, and Ortophon M2 Black. (July 2008).Imagine a Room Full of Mirrors. This page examines some of the effects of domestic room acoustics and human perception. In particular, it considers factors that mean many of us probably don't need very powerful amplifiers! (August 2008).Ohm Improvements. This page looks at the transmission line properties of some loudspeaker cables. Microwave, RF, and comms engineers are often concerned to ensure that cables have an impedance that matches that of the source and load. Meeting that requirement makes good sense in many professional situations. So the page looks at that idea in the context of domestic audio and finds that simpler ideas of cable series resistance and inductance may well be a more useful guide in such circumstances. (November 2008).Ohm and Away. This page continues the investigation into loudspeaker cables. In particular it has a look at the RF properties of cables when combined with an output load to see what demands this can impose on the power amplifier. This page and the previous one (Ohm Improvements) are based on an analytical approach, not on a lumped element approximation, so the results should be more accurate than many other examinations. (December 2008)Taking the Lead. This article presents a set of measurements on the properties of a variety of types of loudspeaker cable. The results are then used to determine the electrical properties. This allows users to assess any effects the cables may have on aspects of performance like amplifier stability and system frequency response. (July 2009)Sound Computing. This page reports how I got on when I started using a computer to play soundfiles, etc. The systems I chose use the Ubuntu and Xubuntu Linux operating system. (October 2009)Listen Again! This page continues to look at the use of the above Ubuntu Linux based approach to audio. In this case it investigates the use of the BBC iPlayer, how to obtain optimum sound quality, and some measurements of the iPlayer output. (November 2009)iPlayer versus DTTV. This article looks at the measureable differences between the BBC iPlayer output and that provided via DTTV. In particular it compares the R3 iPlayer stream with R3 via DTTV. It also uses the 2009 Proms as a chance to compare the results via BBC TV on DTTV with R3. Some of the results were unexpected! (Jan 2010)RF Interference and mains cables. Various types of audiophile mains cables are claimed to have some affect on the sound quality as a result of being able to act as device to reduce the level of RF interference entering domestic audio equipment. The article looks at the RF behaviour of cables to investigate the reliability of this idea. (Mar 2010)Mains filters. Many audiophile mains filters are on offer to audio enthusiasts. These come in a confusing variety of types covering a large price-range. To help people make an informed choice I have written a couple of pages that explain the basics of how the common types of mains filters work. The first page looks at filters using standard passive components. A second page looks at the use of special materials and devices. (July 2010)Tascam HD P2 Recorder. I recently decided to try out this for making recordings from analogue and digital sources and am very pleased with the results. The page shows the results of some test measurements I made using high sample rates. It also documents the details of the BWF headers in the HD P2 recordings. (Aug 2010)A simple DAC for headphone listening. This was initially produced because I wanted a convenient battery powered portable DAC to let me use headphones with various digital sources. However I decided to see if I could produce a design that was portable, inexpensive, and easy to build even if the maker lacked experience with electronics. (December 2010)Time Travel and More is Less. During the 2010 Proms the BBC ran an experiment to stream the concerts from their iPlayer using an XHQ high bitrate of 320kb/sec AAC. The test has two main purposes. Firstly, to find out if listeners felt the results sounded better than the standard R3 iPlayer. Secondly, to test the ability of their Coyopa system (and the internet!) to reliably stream the higher rates to many listers. I took the opportunity to examine the technical performance. These two webpages show the results of my measurements and analysis. (February 2011)Getting a Good Reception 2011. This page may help you assess the quality of DAB and VHF reception you could get in your area, and see how the quality of coverage varies around Britain. It provides maps of the DAB and VHF/FM transmitter locations and powers. It also provides some other information to explain the differences in behaviour between DAB and VHF/FM reception. (April 2011)Time for a Change? This page examines how smoothly audio data is transferred via USB. It employs a new test method I have called the IQ-Test . The results show a clear improvement when a Halide Design USB-SPDIF Bridge is used to transfer data from a computer to a DACMagic. A second page explains in detail how the IQ-Test works. (June 2011)Proms 2011 iPlayer Still Rules. As in previous years I used the Proms to compare the audio via various routes. This year I included both DAB and DSAT TV for the first time. The BBc iPlayer still comes out well. But the results showed up a few surprises and puzzles... (March 2012) The BBC, PCM and NICAM. People tend to think of FM radio as analogue . But in reality, BBC broadcasts have relied on digital technology for decades. Their engineers were the pioneers of many significant advances in digital audio. Although many are aware that NICAM was used for TV, the details of its vital role in radio broadcasting are less well known. I hope this page will shine some light on the topic! (June 2012)The HDCD Enigma. High Definition Compatible Discs (HDCDs) are sold by some specialist / audiophile companies. They are said to be able to deliver superior performance to conventional Audio CDs. But they are also sold by some retailers just as if they were normal Audio CDs. So how do they work? Are they really better? And how compatible are they when played on an ordinary CD machine? (November 2012)Son of HeadDAC. I decided it was time I had another go at making a very simple example of a DIY headphone amplifier / DAC that someone with little experience of pratical electronics could build. This time I decided to use a cheap kit as the basis, and modify it to suit. (February 2013)Digital Dividend... or Digital Distress? OfCom have now made arrangements to allow a part UHF band that has been used for TV to be used from now on for 4G (4th Generation mobile). One result is that the UK will be getting many new transmitters that will interfere with TV reception. Estimates vary, but millions of households may be affected. This page looks at the technical problems in detail. (September 2013)Digital Terrestrial TV and 4G. This page provides a map of the DTTV transmitters. The introduction of the 4G mobile services means that many DTTV transmissions are having their frequencies changed to clear part of the UHF band for 4G. The page therefore also provides maps showing which transmitters will be affected, and which ones will use frequencies closest to the new 4G signals. (September 2013)ALSA for Users and NoMoreSilence. ALSA forms the basis of Audio playback and capture on computers using the Linux OS. These pages are aimed at helping audio enthusiasts to set up their Linux computer(s) to play or record music as they prefer. How to take control using ALSA! (November 2013)More music into your computer. This page looks at some examples of USB audio devices suitable for making digital recordings using a computer. The aim being to get results better than from typical generic internal soundcards . The devices I examined all comply with the open USB Audio class 1 or 2 standards. So they should work fine with Linux and RISC OS as well as Windows and Macs. I've also provided their USB connection details along with tests on their performance. (July 2014)High Quality Audio Recording. This page examines using two high-quality USB audio devices to make audio recordings. The devices I tested were a Benchmark ADC1 USB and a P.S. Audio NuWave Phono Convertor. Each gave good results, but the two devices are very different in the features they offer. Decide for yourself which one you might prefer! (yearbook 2014) Golden Age or Golden Wonder? This page looks at the quality of LP pressings from the late 1950s up to today. How do modern LPs compare with ones back to the dawn of stereo? Has any time been a Golden Age for LP? (May 2014) Armstrong 626 renewal. In July 2015 I decided to have my old Armstrong 626 tuner-amplifier refurbished and modified by Mike Solomons. The set originally belonged to Ted Rule who designed the Armstrong 600 range. So to me it is a special set. I think the result looks and sounds excellent. This page gives more details.Audio CD Health Check! This page shows examples of what you can discover if you carry out a statistical analysis of the sample values on some Audio CDs. The results show that the audio on some of them has problems caused by the way they were produced.Flac audio file Health Check! This page shows some of the results of extending the same approach as I used for the CD Health Check to flac files. As with CDs, the results show that not all high resolution flac files make best use of high sample rates or 24-bit samples. The BBC Audio Factory. From the beginning of 2015 the BBC started to change their systems for delivering the iPlayer. This pages looks into the details of the changes and how and why they have been made. The process is expected to continue though 2015. It should lead to better results, but it has been a bumpy ride!Magnetic Myths This page outlines some basic points about the relative behaviour of Moving Coil (MC) and Moving Magnet (MM) types of LP replay cartridge. In particular it compares their potential performance in terms of signal/noise ratio, etc to dispel some myths that sometimes crop up.The following pages are on a variety of audio related topics. They were mostly prompted by discussions on usenet (newsgroups) or by things I have read on the web or in books or magazines.Arcam rDAC IQ Test Results. This pages shows the results of using the IQ Test to measure the timing regularity of the the USB input of the Arcam rDAC. The results show that the rDAC works very well.Over The Top - Revisited! In 2007 I wrote an article on the way digital recordings can require the player/DAC to reconstruct waveforms that have peaks higher than the largest sample value. At the time I focussed on the data on the discs. This new page looks at the performance of some players/DACs and find that many struggle to cope!A Square Deal. A few decades ago audio engineers and reviewers often used squarewaves as a test waveform to help them assess the behaviour of power amplifiers. However in recent years this technique has largely dissapeared. Having recently re-encountered it being used for measurements on loudspeaker cables I decided to have a fresh look at the advantages and snags of squarewave testing.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. Most of the programs I have written for working with soundfiles are for the RISC OS operating system. Some of them are available via the Archive Magazine pages above. However I have recently also started using Linux and the ROX filer/desktop. Hence I have also begun the process of producing ROX/Linux versions of my software. The newest versions of the software - in both RISC OS and ROX/Linux versions - are now available from my software webpage.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.

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