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<!DOCTYPE html> <html lang="en-us"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <link rel="icon" href="http://www.zytrax.com/favicon.ico"> <title>Tech Stuff - Digital Audio/Video</title>   <style type="text/css">  </style> <style type="text/css" media="print">  </style> <script type="text/javascript">  </script> </head> <body>  <div class="l-b">  <a href="http://www.zytrax.com"><img id="toplogo" src="http://www.zytrax.com/images/zytrax-logo-info.png" alt="ZYTRAX Info Logo"></a>  <p class="n-t-t"><a href="http://www.zytrax.com/feedback.htm" class="n-t-sr">mail us</a>  |  <a href="http://www.zytrax.com/run/mailpage.php" class="n-t-sr">mail this page</a></p> <div class="n-t0"> <a href="http://www.zytrax.com/Company/contacts.html" class="n-t-sr">contact us</a> </div> <div class="n-t0"> <a href="http://www.zytrax.com/training/" class="n-t-sr">training</a>  |  </div> <div class="n-t0"> <a href="http://www.zytrax.com/tech/" class="n-t-sr">tech stuff</a>  |  <ul 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href="http://www.zytrax.com/security/" class="t-da">Security</a></li> </ul> </div>  </div>  <div class="l-c"> <p class="adv"> <script type="text/javascript"> </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> </p> <h1>Survival Guide/Tech Stuff - Digital Audio/Video</h1> <p>Digital Audio or Audio/Visual is one of those areas that crosses the border between pure technical knowledge about computer'ish subjects - file formats, bit rates, sampling and all that good solid stuff, and other territory to do with sound frequencies and if the material is musical - tempo and pitch and harmonics and...and .... and the maths - oof! Fast Fourier Transforms (FFT) and RMS and Logarithms - stuff we thought we had long, and mercifully, left behind. We were quite shocked on our first excursion into the depths of this dark and frequently secretive world. And the shock when we discovered that you had to pay for some specifications. And Patents. What a lot of patents. We have only recently recovered.</p> <p><b>Health Warning:</b> These pages are a work in progress and are intended to capture our (very) slowly growing knowledge. At this time we are mostly interested in digital audio. We cover video where we stumble accross something related to audio. Our primary motivation is the preservation and restoration of old recorded music. If you spot an error, omission or incomprehensible description please take the time to write and point it out by using the links at the top or bottom of each page. We always respond in the same spirit in which you write to us.</p> <h3 id="contents">Contents</h3> <table class="p-m-s"> <tr > <td class="t-td1 w-150"><a href="sound.html" class="t-db">Sound Primer</a></td> <td class="t-td2">Fairly quick overview of Frequencies, Notes and Pitch (even ADSR) together with all that Harmonics, Overtones, Fundamentals - and even Partials - stuff, followed by the mystery of Loudness and sound power. Necessary but horrible stuff, just horrible.</td> </tr> <tr > <td class="t-td1"><a href="digital-sound.html" class="t-db">Digital Sound Primer</a></td> <td class="t-td2">Big page. Starts with an overview of analog sound and recording history (well, where would you put it). How audio digitization works, sampling theory (Nyquist), quantization, Time domains, frequency domains, looking at ADSR and harmonics. Lie down in a darkened room for a minimum of 3 hours after reading this.</td> </tr> <tr > <td class="t-td1"><a href="audio.html" class="t-db">Frequencies</a></td> <td class="t-td2">Frequencies of musical notes together with some information about typical instrument (and voice) frequency ranges and other incidental noises that you may come accross in your daily life.</td> </tr> <tr > <td class="t-td1"><a href="equalization.html" class="t-db">Equalization & FFT</a></td> <td class="t-td2">Equalization, with Preferred and Calculated center frequencies (kinda explained). Sound metering (VU and Peak and all that other nonsense) with a description of what we did to code a useful (to us) sound meter. Finally, no discussion of equalization is complete without the good old FFT and boy, do we discuss the FFT. These are notes about our implementation - or 'trying to provide sensible output when they don't tell you stuff'. Headache inducing page, and big, very big. But useful, if you like this kind of thing.</td> </tr> <tr > <td class="t-td1"><a href="formats.html" class="t-db">Files & Codecs</a></td> <td class="t-td2">Quick overview of files, codecs and containers - all that alphabet soup of AAC, HE-AAC, AIFF, MP3, MPEG, m4a stuff. Pretty complete - well, the more inportant ones anyway - but not exhaustive.</td> </tr> <tr > <td class="t-td1"><a href="calculator.html" class="t-db">Acoustic Calculators</a></td> <td class="t-td2">Note frequency to various decimal plates and user defined A4 pitch frequency. Preferred and Calculated (band) frequencies for a user defined range of octave values (1 to 1/48). FFT/DFT duration, center and band frequencies for a FFT/DFT size, sample size and bit-depth. Heady stuff. Not for the faint hearted. But jolly good fun.</td> </tr> <tr > <td class="t-td1"><a href="glossary.html" class="t-db">Glossary</a></td> <td class="t-td2">Some stuff we picked up along the way. Just another one of the 10 million audio glossaries available on the web.</td> </tr> <tr > <td class="t-td1"><a href="windows7.html" class="t-db">Audio on Windows 7</a></td> <td class="t-td2">We had a lot - a lot - of trouble to get a glitch free audio playback on a Windows 7 laptop. Turns out we were not alone. This is how we fixed it. While the specific actions may not work for you we focus on the methodology we used which should work for everyone. It may even work on Windows 10/11 though we have not tried it.</td> </tr> </table> <h2 id="needs">Our History, Needs and Plans for Digital Audio/Visual</h2> <p><b>History:</b> The Digital Audio project is partly professional, partly hobby. We started trying to restore a number of digital audio tracks that had mostly been captured from very old 78 RPM records, occasionally vinyl, but mostly good old 78's (shellac) in the majority of cases from the 1920's, 30's and 40's. In some cases we had access to the source material and could re-capture but mostly not. We had what we had and were expected to perform miracles. Which, as we all know, can take a bit of time. Professionally we are increasingly involved with some serious IPTV work which is bringing more visual stuff into the picture and which will, over time, be increasingly reflected in the content of this section.</p> <p>We started to use Audacity and that took us a long way. The noise removal and audio repair functions are very impressive. Then we moved into <a href="glossary.html#equalization" class="t-db">equalization</a> in order to try and improve sound quality. We made some bad mistakes here. But since we always kept the original files nothing catastrophic occurred - we could always start again. But there are limits to Audacity when using some services - that does not detract in any way from the excellent quality and functionality for many, many other purposes and we still regularly use it. In particular we found that the batch mode of spectrum analysis extremely limiting. Of necessity it uses an averaging method to compute the spectrum graph and initially this was sufficient.</p> <p>Then we got greedy. We wanted to be able to see the dynamic frequency. So we experimnted with a number of real time frequency analysers. Then we got very unhappy - some used 9 bands, 7 bands, 12 bands. Some use green and red leds to show intensity (what's intensity and does that relate to loudness). Almost none provided any useful documentation of their selected frequency bands or the reasons for the colors. Some came with equalizers which almost never were tied to their frequncy displays. A 10 band frequency analyzer with a three position equalizer (bass, middle and treble) is not too exciting especially when it does not even define the cut-offs for each range. Seemed this was more of an art form than a serious endeavour - not that artists are not serious people. Some of them are extremely serious.</p> <p>If we were prepared to pay $gazillions we could get all we wanted. But we were not. So we finally found a reasonably spec'd Open Source player with what looked like a decent equalizer. So using our ears as a frequency analyzer (not too reliable) we played with that and it took us further down the road.</p> <p>Finally we got past greedy - we got gluttonous. What we really wanted was:</p> <ol> <li>A real-time frequency analyzer with at least 1/3 octave (31 bands).</li> <li>The ability to drill-down even further within one or more 1/3 octaves - 1/12 octave or even lower</li> <li>VU-Meter/PPM with peak detection showing on a dB (SPL) scale not these meaningless undimensioned scales of the original meters. These was an excuse 70 years ago when this stuff was originally developed but not today.</li> <li>An equalizer that would reflect directly the frequency analyzer (1/3 or lower). The idea being that we could set the equalizer directly on top of the frequency analyzer display and fool around with it in real-time.</li> <li>A hard limiter on the equalizer, so we could set the gain level but be able to cap it for any given frequency or accross all frequencies.</li> <li>The ability to save the equalizer settings as a profile that could be recalled in various ways including merging multiple equalization profiles.</li> <li>An equalizer that would be optionally harmonic sensitive - we could construct a profile so that if we were picking up (amplifying),say, a violin we could define a harmonic profile that would automatically apply proportional gain to the first, second etc. harmonics. Eventually we could build a series of these and call up one or more, for example, boost the violins by, say, 6 dB(SPL) and reduce the violas by, say, 4 dB(SPL). In real-time.</li> <li>We wanted to be able to change equalizer settings at various times within a track. Thus the ability to have multiple equalizer profiles that we could set against the track time. Use equalizer profile 1 until 35 seconds, then switch to profile 7 until 1 minute 47 seconds etc., etc..</li> <li>Since in our old recordings we felt that we had some rogue frequencies we wanted an equalizer that could move through a selected range (scan) and knock out (or boost) one frequency range at a time (with or without harmonics) to see the effect.</li> <li>Since much of the material we were working with had, at best, a dubious provenance and had probably been disatrously mangled - possibly even by us in an earlier life we needed the ability to 'clean' such material. While term 'enhancer' is widely used to describe multiple capabilities we wanted the ability to restore the instrument characteristics. In short, given an intrument's starting point (not always a simple thing to identify) the 'enhancer' would add or adjust harmonic frequencies based on that instrument's characteristics - including its ADSR profile.</li> <li>Clearly we wanted to able to both playback the effects in real-time and/or capture to a file in at least WAV and FLAC format (we could subsequently convert to any other format required) once we were happy.</li> </ol> <p>None of this seems too, too unreasonable and some of it is pure speculation on our part that it will yield the reults we want. At this time we have decided that we need to develop our own tool-set. We like Open Source but will release our code under the more permissive BSD/MIT license rather than GNU GPL. These pages are the result of our current development work and our pathetic, plodding and unbearably slow aquisition of knowledge (well that's how we like to characterize it) in audio and visual processing.</p> <p>Don't hold your breath waiting for this stuff to appear.</p> <hr> <p class="p-m-n"><br>Problems, comments, suggestions, corrections (including broken links) or something to add? Please take the time from a busy life to 'mail us' (at top of screen), the webmaster (below) or <a href="javascript:mailus('info-support','zytrax.com','Support Issue')" class="t-db">info-support at zytrax</a>. You will have a warm inner glow for the rest of the day.</p>  </div> <div class="l-l">  <div class="n-l"> <p class="c-g t-b t-o m-h5 t-r">Tech Stuff</p>  <ul class="n-l1p"> <li class="n-l1p-e"> <a href="http://www.zytrax.com/tech" class="n-l-c">tech home</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Digital Audio - primers, calculators, equalization, frequency tables, file formats, glossary - a mere splash in the ocean" href="http://www.zytrax.com/tech/audio/" class="n-l-c">audio stuff</a> <ul class="n-l2"> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/sound.html" class="n-l-f">sound primer</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/digital-sound.html" class="n-l-f">digital primer</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/audio.html" class="n-l-f">note frequencies</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/equalization.html" class="n-l-f">eq, meters & fft</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/calculator.html" class="n-l-f">calculators</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/formats.html" class="n-l-f">files & codecs</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/audio/glossary.html" class="n-l-f">glossary</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Browser IDs, SSIs, Apache Configuration, regular expressions" href="http://www.zytrax.com/tech/web/" class="n-l-c">web stuff</a> <ul class="n-l2"> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/web/browser_ids.htm" class="n-l-f">browser ids</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/web/mobile_ids.html" class="n-l-f">mobile_ids</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/web/env_var.htm" class="n-l-f">apache env vars</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/web/ssi.htm" class="n-l-f">apache ssi</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/workarounds.html#popout" class="n-l-f">css popout menus</a></li> <li class="n-l2-e"><a title="most of those annoying HTML entity codes that we forget all the time" href="http://www.zytrax.com/tech/web/entities.html" class="n-l-f">html entities</a></li> <li class="n-l2-e"><a title="Decimal to Hexidecimal to Binary conversion - even Octal!" href="http://www.zytrax.com/tech/protocols/hex.html" class="n-l-f">dec > hex > bin</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a href="http://www.zytrax.com/tech/dom/" class="n-l-c">dom stuff</a><br> <ul class="n-l2"> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/dom/guide.html" class="n-l-f">dom guide</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/dom/w3c_dom.html" class="n-l-f">page explorer</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/dom/navigate.html" class="n-l-f">dom navigation</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="CSS is about a lot more than STYLE. Wheezes, table-less layouts, CSS pop-ups, CSS Shortcuts" href="http://www.zytrax.com/tech/css/" class="n-l-c">css stuff</a> <ul class="n-l2"> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/layoutnotes.html" class="n-l-f">css liquid design</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/workarounds.html#popout" class="n-l-f">css popout menus</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/workarounds.html" class="n-l-f">css notes</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/syntax.html" class="n-l-f">css syntax</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/css/shortcut.html" class="n-l-f">css short-forms</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="includes PHP, Ruby and some Java stuff (all about obscure solutions to stupid problems)" href="http://www.zytrax.com/tech/lang/" class="n-l-c">language stuff</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="quick overview 'cos we always forget - not that we ever knew much - now includes a nifty browser-based tester" href="http://www.zytrax.com/tech/web/regex.htm" class="n-l-c">regex stuff</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="rfc ordered by subject" href="http://www.zytrax.com/tech/rfcs/" class="n-l-c">rfc stuff</a> <ul class="n-l2"> <li title="dns rfcs" class="n-l2-e"><a href="http://www.zytrax.com/books/dns/apd/" class="n-l-f">dns rfcs</a></li> <li title="ldap rfcs" class="n-l2-e"><a href="http://www.zytrax.com/books/ldap/apc/" class="n-l-f">ldap rfcs</a></li> <li title="ipv6 rfcs" class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/ipv6.html#rfcs" class="n-l-f">ipv6 rfcs</a></li> <li title="tls/x.509 rfcs" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/ssl.html#rfcs" class="n-l-f">tls/x.509 rfcs</a></li> <li title="some other subjects - we only update these when we are active - some lists are consequently long in the tooth" class="n-l2-e"><a href="http://www.zytrax.com/tech/rfcs" class="n-l-f">other rfcs</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="TCP/IP, IPv4, IPv6, ISDN, LAN, VoIP, ITU Multi-Media" href="http://www.zytrax.com/tech/protocols/" class="n-l-c">protocol stuff</a> <ul class="n-l2"> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/tcp.html" class="n-l-f">tcp, udp, icmp</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/ip-classes.html" class="n-l-f">ipv4</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/ipv6.html" class="n-l-f">ipv6</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/isdn/" class="n-l-f">isdn</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/ssl.html" class="n-l-f">ssl/tls/x.509</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/ss7/" class="n-l-f">ss7 &sigtran</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/protocols/lan/" class="n-l-f">802.3 lan</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="PC Parallel Ports, LAN wiring, RS232, Centronics, DIN" href="http://www.zytrax.com/tech/layer_1/" class="n-l-c">cable stuff</a> <ul class="n-l2"> <li title="10baseT, 100base-TX/T4, 1000baseT, 10Gbase-T, RJ45, STP" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm" class="n-l-f">lan pinouts</a></li> <li title="mixing telephony and 802.3 LAN can be done on cat5/5e/6 wiring" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/mixed.html" class="n-l-f">lan & telephone</a></li> <li title="RS 232 pinouts on db9, db24 and T1" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm" class="n-l-f">rs232 pinouts</a></li> <li class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/heavy.htm" class="n-l-f">serial primer</a></li> <li title="USB 2.0, 3.0, 3.1 and 3.2 plus Firewire (i.Link) IEE 1394" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/serial.html" class="n-l-f">usb & firewire</a></li> <li title="some information about display and monitors/console interfaces inclusing VGA, HDMI, DVI and Thunderbolt" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/monitors.htm" class="n-l-f">displays</a></li> <li title="modular jack is the term we should use for those telephone and lan connectors" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/cables_jacks.htm" class="n-l-f">modular jacks</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="10baseT, 100base-TX/T4, 1000baseT, 10Gbase-T, RJ45, STP" href="http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm" class="n-l-c">lan wiring</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="DB9, DB25 pinouts, RJ45 serial, T1 and RS standards alphabet soup" href="http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm" class="n-l-c">rs232 wiring</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Decimal to Hex and Binary conversion table - even a description of Octal!" href="http://www.zytrax.com/tech/protocols/hex.html" class="n-l-c">dec > hex > bin</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="character sets ain't as simple as they look" href="http://www.zytrax.com/tech/codes.htm" class="n-l-c">character sets</a> <ul class="n-l2"> <li title="pretty much all the characters sets in the known universe including utf-7, 8 and 16" class="n-l2-e"><a href="http://www.zytrax.com/tech/characters/" class="n-l-f">character sets</a></li> <li title="ascii variant of international reference alphabet 5 (ira5)" class="n-l2-e"><a href="http://www.zytrax.com/tech/codes.htm" class="n-l-f">ascii codes</a></li> <li title="international reference alphabet 5 (ascii's cousin)" class="n-l2-e"><a href="http://www.zytrax.com/tech/ia5.html" class="n-l-f">ia5 codes</a></li> <li title="all that ™ & © stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/web/entities.html" class="n-l-f">html entities</a></li> <li title="silly page containing a bunch of fonts in various sizes including your PCs defaults" class="n-l2-e"><a href="http://www.zytrax.com/tech/web/fonts.html" class="n-l-f">web fonts</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="The T series, E series and J series and then all that optical stuff (OC-12 etc.)" href="http://www.zytrax.com/tech/data_rates.htm" class="n-l-c">data rate stuff</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Even us electronic guys gotta know how to screw it together, if you get our drift" href="http://www.zytrax.com/tech/mech/" class="n-l-c">mechanical stuff</a> <ul class="n-l2"> <li title="fastener (screw) head styles - surprising number of choices" class="n-l2-e"><a href="http://www.zytrax.com/tech/mech/heads.htm" class="n-l-f">head styles</a></li> <li title="threads for imperial (UNF, UNC) & metric sizes" class="n-l2-e"><a href="http://www.zytrax.com/tech/mech/threads.htm" class="n-l-f">threads</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="A collection of howtos including Samba3 as PDC, FreeBSD firewalls" href="http://www.zytrax.com/tech/howtos/" class="n-l-c">howto stuff</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="A collection of survival guides - quick overviews - to popular software" href="http://www.zytrax.com/tech/survival/" class="n-l-c">survival stuff</a> <ul class="n-l2"> <li title="tls and x.509 (ssl) certificates - warning: headache inducing stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/ssl.html" class="n-l-f">ssl/tls/x.509</a></li> <li title="Abstract Syntax Notation. 1 (ASN.!) and Distinguished Encoding Rules (DER) - not for the faint hearted. Pass the pain medication, we feel a headache coming on." class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/asn1.html" class="n-l-f">ASN.1 & DER</a></li> <li title="Kerberos is great - but tough, oh my, tough stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/kerberos.html" class="n-l-f">kerberos</a></li> <li title="We've used postfix for years but always forget which of the 27 million parameters to use" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/postfix.html" class="n-l-f">postfix</a></li> <li title="Symetric, asymetric, MACs, hashes - eye watering stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/encryption.html" class="n-l-f">encryption</a></li> <li title="Just what time is it in Kuala Lumpur, and what's that got to do with cron?" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/cron.html" class="t-db">cron</a></li> <li title="Gotta love wxWidgets - free, fantastic, flexible - but hard to see the wood for the trees sometimes" class="n-l2-e"><a href="http://www.zytrax.com/tech/survival/wxwidgets.html" class="n-l-f">wxWidgets</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Our wireless overview, Calculators, Fresnel zones, links to 'heavy' stuff, some early 802.11 stuff (mostly wi-fi related)" href="http://www.zytrax.com/tech/wireless/" class="n-l-c">wireless stuff</a> <ul class="n-l2"> <li title="our irreverent general intro to wirelss - purist will not like this page" class="n-l2-e"><a href="http://www.zytrax.com/tech/wireless/intro.htm" class="n-l-f">overview</a></li> <li title="wireless calculators for system budgets, free-space loss, fresnel effects and a bunch of other stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/wireless/calc.htm" class="n-l-f">calculators</a></li> <li title="fresnel effect explanation - well, we can understand it" class="n-l2-e"><a href="http://www.zytrax.com/tech/wireless/fresnel.htm" class="n-l-f">fresnel effects</a></li> <li title="our outrageously biased description of frequency hopping versus direct sequence for spread spectrum" class="n-l2-e"><a href="http://www.zytrax.com/tech/wireless/fh_ds.htm" class="n-l-f">fh vs ds</a></li> <li title="some terminology covering 802 standards and modulation techniques" class="n-l2-e"><a href="http://www.zytrax.com/tech/wireless/soup.html" class="n-l-f">wireless soup</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Pinouts - USB, DIN, Firewire, VGA, DVI, HDMI, DisplayPort and Thunderbolt, I/O interface speeds, Screen sizes including HD" href="http://www.zytrax.com/tech/pc/" class="n-l-c">pc stuff</a> <ul class="n-l2"> <li title="din and mini-din for older PCs" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/din.htm" class="n-l-f">din & mini-din</a></li> <li title="802.3 LAN stuff" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm" class="n-l-f">802.3 lan</a></li> <li title="connection of monitors has changed over the years from clunky VGA to svelte HDMI - all the pinouts you could hope for" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/monitors.htm" class="n-l-f">monitor pinouts</a></li> <li title="serial (db9, db24) connections - slow but trusty" class="n-l2-e"><a href="http://www.zytrax.com/tech/layer_1/cables/tech_rs232.htm" class="n-l-f">serial stuff</a></li> <li title="usb pinouts and descriptions of power levels for usb 1, 2 and 3 - also includes firewire" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/serial.html" class="n-l-f">usb & firewire</a></li> <li title="pc interfaces are changing and getting faster - we can never keep up - list of interfaces and their speeds" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/interfaces.html" class="n-l-f">pc interfaces</a></li> <li title="we get confused about most things - just what is 1080p - pc and tv screen resolution table with some explanations" class="n-l2-e"><a href="http://www.zytrax.com/tech/pc/resolution.html" class="n-l-f">screen resolutions</a></li> </ul> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Electronic glossary, some old experiments with 3.3/5V protection and early BGA designs" href="http://www.zytrax.com/tech/electronics/" class="n-l-c">electronic stuff</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="ragbag collection of links that we publish from time to time - maybe useful, maybe not" href="http://www.zytrax.com/links" class="n-l-c">tech links</a> </li> </ul> <ul class="n-l1p"> <li class="n-l1p-e"> <a title="Our DNS and LDAP for Rocket Scientists guides" href="http://www.zytrax.com/books" class="n-l-c">open guides</a> <ul class="n-l2"> <li title="dns for rocket scientists" class="n-l2-e"><a href="http://www.zytrax.com/books/dns/" class="n-l-f">dns guide</a></li> <li title="ldap for rocket scientists" class="n-l2-e"><a href="http://www.zytrax.com/books/ldap/" class="n-l-f">ldap guide</a></li> </ul> </li> </ul> <p class="t-r"> <a title="RSS (2.0) Feed - right click on icon, select 'Copy Link URL' or 'Copy Shortcut', paste into RSS Feed Reader, or drag and drop into RSS Feed Reader" href="http://www.zytrax.com/zytrax.rss" class="n-l-c"><img class="w-32 center" src="http://www.zytrax.com/images/rss.png" alt="RSS Feed Icon"></a> </p> <p class="p-b-h t-r">If you are happy it's OK - but your browser is giving a less than optimal experience on our site. You could, at no charge, upgrade to a W3C standards compliant browser such as <a href="http://www.mozilla.org" class="t-db">Firefox</a></p> </div> </div> <div class="l-r">  <div class="w-150">  <p class="c-g t-b t-o m-h8">Search</p> <form class="f-b-n" method="get" action="http://www.google.com/custom" target="_top"> <table> <tr> <td style="white-space: nowrap"> <input type="hidden" name="domains" value="www.zytrax.com"> <input class="b-lg" type="text" name="q" size="16" maxlength="255" value=""> </td></tr> <tr> <td style="white-space: nowrap"> <table> <tr> <td> <input type="radio" name="sitesearch" value="" checked="checked"><span class="t-s">web</span> </td> <td> <input type="radio" name="sitesearch" value="www.zytrax.com" ><span class="t-s">zytrax.com</span> </td> </tr> </table> <input class="b-lg" type="submit" name="sa" value="Google Search"> <input type="hidden" name="client" value="pub-9419480011552853"> <input type="hidden" name="forid" value="1"> <input type="hidden" name="ie" value="ISO-8859-1"> <input type="hidden" name="oe" value="ISO-8859-1"> <input type="hidden" name="safe" value="active"> <input type="hidden" name="cof" value="GALT:#008000;GL:1;DIV:#336699;VLC:663399;AH:center;BGC:FFFFFF;LBGC:336699;ALC:0000FF;LC:0000FF;T:000000;GFNT:0000FF;GIMP:0000FF;LH:50;LW:355;L:http://www.zytrax.com/images/zytrax-info-google.gif;S:http://www.zytrax.com/tech;FORID:1;"> <input type="hidden" name="hl" value="en"> </td></tr></table> </form>   <div class="t-h"><p><span class="t-g">Share</span></p> <div class="t-h-1"> Icons made by <a href="https://www.flaticon.com/authors/icomoon" title="Icomoon">Icomoon</a> from <a href="https://www.flaticon.com/" title="Flaticon">www.flaticon.com</a> is licensed by <a href="http://creativecommons.org/licenses/by/3.0/" title="Creative Commons BY 3.0" target="_blank">CC 3.0 BY</a></div></div> <a href="http://www.facebook.com/share.php?u=http://www.zytrax.com/tech/audio/&h=Tech%20Stuff%20-%20Digital%20Audio/Video"><img class="w-32" title="add page to facebook" src="http://www.zytrax.com/images/facebook.png" alt="share page via facebook"></a> <a href="http://twitter.com/home/?status=Useful%20page%20http://www.zytrax.com/tech/audio/"><img class="w-32" title="tweet this page" src="http://www.zytrax.com/images/twitter.png" alt="tweet this page"></a> <p class="c-g t-b t-o m-h5">Page<p> <a class="a-n" href="http://www.zytrax.com/feedback.htm"><img class="w-32" title="Page comment feature" src="http://www.zytrax.com/images/mail.png" alt="email us"></a> <a class="a-n" href="http://www.zytrax.com/run/mailpage.php"><img class="w-32" title="Send to a friend" src="http://www.zytrax.com/images/mailfriend.png" alt="Send to a friend feature"></a> <a class="a-n" href="#" onclick="window.print();return false;"><img class="w-32" title="print page" src="http://www.zytrax.com/images/printpage.png" alt="print this page"></a> <a class="a-n" title="View page full width - suppresses left and right hand menus" href="http://www.zytrax.com/tech/audio/?pf=yes"><img class="w-32" src="http://www.zytrax.com/images/fullwidth.png" alt="Display full width page"></a> <a class="a-n" href="#" onclick="fontchange('d');return false;"><img class="w-32" title="Decrease font size" src="http://www.zytrax.com/images/smaller.png" alt="Decrease font size"></a> <a class="a-n" href="#" onclick="fontchange('i');return false;"><img class="w-32" title="Increase font size" src="http://www.zytrax.com/images/bigger.png" alt="Increase font size"></a> <p class="c-g t-b t-o m-h5">Software</p> <p class="m-h5"> <a title="Audacity. Terrific Open Source Sound Editor. Cross platform. We are big fans" href="http://audacity.sourceforge.net/" target="_blank">Audacity</a><br> </p> <p class="c-g t-b t-o m-h5">Theory Stuff</p> <p> <a title="Some great backgrounders - we almost understood FFT after reading the article here - almost" href="http://www.earlevel.com/Digital%20Audio/index.html" target="_blank">Filters, FFT and more</a><br> <a title="Terrific Digital signal processing Introduction" href="http://www.rane.com/note134.html" target="_blank">Signal Processing</a><br> <a title="Great Reference and Glossary" href="http://www.rane.com/par-a.html" target="_blank">Audio glossary</a><br> <a title="Gruesome mathematical algorithms - some are even essential for digital audio/DSP - shudders" href="http://www.nrbook.com/a/bookcpdf.php" target="_blank">Numeric Algorithms</a><br> <a title="Useful collection of acoustic stuff from the University of New South Wales in Australia" href="http://www.phys.unsw.edu.au/jw/basics.html" target="_blank">UNSW Acoustics Info</a><br> <a title="Extensive explanation of the decibel from the University of New South Wales in Australia" href="http://www.phys.unsw.edu.au/jw/basics.html" target="_blank">UNSW - Dreaded Decibel</a><br> <a title="Good - if a tad wordy at times - explanation of a lot of acoustic attributes - with plenty of maths in some sections for those who revel in that stuff" href="http://www.silcom.com/~aludwig/contents.htm" target="_blank">Acoustic Explanations</a><br> <a title="Free download of introduction to the FFT - very readable" href="http://www.fftguru.com" target="_blank">FFT Primer and Book</a><br> <a title="A very useful paper on the DFT/FFT - the section on handling the FFT output is a masterpiece of simplicity and clarity. Boiled down to the essence. No higher praise in our view." href="http://www.staff.vu.edu.au/msek/Frequency%20Analysis%20-%20FFT.pdf" target="_blank">FFT Output</a><br> <a title="There is even an Open Source FFT library - is there no end to life's mysteries and joys" href="http://www.fftw.org/" target="_blank">FFTW</a><br> </p> <p class="c-g t-b t-o m-h5">Interesting Stuff</p> <p> <a title="Excellent detail material on optimizing L.A.M.E and Ogg Vorbis files for a variety of conditions - especially FM quality" href="http://jthz.com/mp3/">MP3/OGG Stuff</a><br> <a title="Wonderful site with samples of notes played on a variety of instruments - but no bandoneon - sigh - site not available when we last checked" href="http://theremin.music.uiowa.edu/MIS.html">Instrument Samples</a><br> </p> <p class="c-g t-b t-o m-h5">Our Stuff</p> <p> <a title="Some basic stuff" href="index.html">Intro and Overview</a><br> <a title="Quick waltz through the alphabet soup of MP3, AAC, WAV, FLAC, WMA etc. with varying degrees of detail, includes meta (ID3) data and other formats" href="formats.html">A/V Formats</a><br> <a title="Musical Notes and Frequencies, Instrument frequency ranges, Pitch, Harmonics and Overtones" href="audio.html">Audio Frequencies</a><br> <a title="Mostly analog but with strong emphasis on its applicability in the digital world includes - Pitch, Harmonics, Overtones, Partials, Loudness and all that good stuff" href="sound.html">Sound Primer</a><br> <a title="A primer on digital sound. Sound waves, recording history, sound digitization, Time Domain and Frequency domain and some other brain hurting stuff" href="digital-sound.html">Digital Sound</a><br> <a title="Collection of stuff about equalization - principles, n-band equalizers, center frequencies, frequency analysers, harmonic equalizers and enhancers. Code sample for our Peak Detecting Sound meter. Using the FFT for audio signal analysis and generating useful information." href="equalization.html">Equalization, Meters, FFT</a><br> <a title="Calculate musical notes based on octave number, EQ centre and band frequencies for multiple and fractional octave ranges" href="calculator.html">Acoustic Calculator</a><br> <a title="Audio meta/tag data is, in our view, a mess. This is our modest proposal to solve the problem" href="audio-meta.html">Audio Meta Data</a><br> <a title="We had a lot of trouble - a lot - to get hiccup free audio on our Windows 7 laptop - seems we were not alone. This is how we fixed it" href="windows7.html">Win7 Audio Problems</a><br> <a title="Our 'constantly under construction' audio glossary - just to add to the 10 million others out there" href="glossary.html">Audio Glossary</a><br> </p> </div> <p class="c-g t-b t-o">Site</p> <a class="a-n" href="http://www.zytrax.com/about_site.htm#css"><img class="w-32" src="http://www.zytrax.com/images/css.png" alt="CSS Technology"></a> <a class="a-n" href="http://www.zytrax.com/security/spf.html"><img title="SPF Record Conformant Domain" class="w-32" src="http://www.zytrax.com/images/spf.png" alt="SPF Record Conformant Domain"></a> </div> <div class="l-f">  <table> <tr> <td class="p-f-s t-l"> Copyright © 1994 - 2025 ZyTrax, Inc.<br> All rights reserved. <a href="http://www.zytrax.com/legal.html" class="p-f-s">Legal</a> and <a href="http://www.zytrax.com/privacy.html" class="p-f-s">Privacy</a> </td> <td class="t-c"><a href="https://www.zytrax.com" target="_blank" class="p-f-s">site by zytrax</a><br> <a href="https://www.javapipe.com" target="_blank" class="p-f-s">hosted by javapipe.com</a></td> <td class="p-f-s t-r"> <a href="javascript:mailus('web-master','zytrax.com','About Web site')" class="p-f-s">web-master at zytrax</a><br> Page modified: February 10 2025. </td> </tr> </table> </div>   </body> </html>