====== Audio Signal Visualisation and Measurement ====== ~~SLIDESHOW~~ Robin Gareus\\ linuxaudio.org\\ CiTu, Université Paris\\ ===== Part I - Audio Signal Meters ===== {{ :wiki:a3mixer.png |}} ===== Why measure ? ===== \\ * When tracking, meters are used to ensure that input signals do not overload and maintain reasonable headroom. ===== Why measure ? ===== \\ * When tracking, meters are used to ensure that input signals do not overload and maintain reasonable headroom. * Meters offer a quick visual indication of activity when working with a large number of tracks. ===== Why measure ? ===== \\ * When tracking, meters are used to ensure that input signals do not overload and maintain reasonable headroom. * Meters offer a quick visual indication of activity when working with a large number of tracks. * During mixing, meters provide a rough estimate of the loudness of each track. ===== Why measure ? ===== \\ * When tracking, meters are used to ensure that input signals do not overload and maintain reasonable headroom. * Meters offer a quick visual indication of activity when working with a large number of tracks. * During mixing, meters provide a rough estimate of the loudness of each track. * At the mastering stage, meters are used to check compliance with upstream level and loudness standards, and to optimise the dynamic range for a given medium. ===== What to measure ? ===== \\ \\ * Focus on **medium**: highlight digital number, or analogue level constraints. ===== What to measure ? ===== \\ \\ * Focus on **medium**: highlight digital number, or analogue level constraints. * Focus on **message**: provide a general indication of loudness as perceived by humans. ===== What to measure ? ===== \\ \\ * Focus on **medium**: highlight digital number, or analogue level constraints. * Focus on **message**: provide a general indication of loudness as perceived by humans. * Focus on **interoperability**: strict specification for broadcast. ===== Types of Meters ===== \\ * **DPM** (digital peak meter) displays the absolute maximum signal of the raw audio PCM signal. Focus on **medium**. ie. digital numbers, and Analog/Digital converters. ===== Types of Meters ===== \\ * **DPM** (digital peak meter) displays the absolute maximum signal of the raw audio PCM signal. Focus on **medium**. ie. digital numbers, and Analog/Digital converters. * **RMS** (root mean square) type meters provide a general indication of loudness as perceived by humans. It emphasizes on the **message** as opposed to technical, medium related parameters. ===== Types of Meters ===== \\ * **DPM** (digital peak meter) displays the absolute maximum signal of the raw audio PCM signal. Focus on **medium**. ie. digital numbers, and Analog/Digital converters. * **RMS** (root mean square) type meters provide a general indication of loudness as perceived by humans. It emphasizes on the **message** as opposed to technical, medium related parameters. * **IEC** type meters are a mix between DPM and RMS, created mainly for the purpose of interoperability. (broadcast instustries: BBC, EBU) ===== On Measurements - An analogy ===== \\ {{ :wiki:rulers.png |}} ===== On Measurements - An analogy ===== \\ {{ :wiki:rulers.png |}} {{ :wiki:borked_rulers2.png |}} ===== On Measurements - An analogy ===== \\ {{ :wiki:rulers.png |}} {{ :wiki:borked_rulers2.png |}} {{ :wiki:borked_rulers1.png |}} ===== On Measurements ===== \\ \\ The whole point of measuring things is to be able to meaningfully compare the reading of the meter to that of another [similar] meter. ===== On Specs (1/2) ===== \\ \\ The IEC specs are designed such that all meters complying with the specs, even when using completely different implementations, will produce identical results. ===== On Specs (2/2) ===== \\ \\ * Audio Level Meters are standardized (IEC, ITU, IEEE, DIN, BBC,...) * Due to historical and commercial reasons various standards exist * The scale of [most] meters is logarithmic (dB) * Different types - Medium vs. Content. ===== Key Characteristics of Audio Level Meters ===== \\ \\ * Alignment or Reference Level and Range * Ballistics (rise/fall times, peak-hold, burst response) * Frequency Response (filtering) ===== VU meter specs (ASA C16-5-1942) ===== * "The reading shall be 0 VU when for an AC voltage equal to 1.228 Volts RMS across a 600 Ohm resistance" * "The rise time, defined as the time it takes for the needle to reach 99% of the distance to 0 VU when the VU-meter is submitted to a signal that steps from 0 to a level that reads 0 VU, is 300 ms." * "The fall time is the same as the rise time" * "The overshoot must be within 1 to 1.5%." * "The reading must not depart from the reading at 1kHz by more 0.5 dB between 25 Hz and 16 kHz." ===== Presonus Tube Pre - a VU meter toy ===== {{ http://robin.linuxaudio.org/tmp/vu_tp.webm }} * incorrect deflection (not to scale) * not useful for measurements (but it looks cool :) ===== Two Commercial Plugins - digital VU toys ===== {{ http://robin.linuxaudio.org/tmp/vu-010.webm }} * [[http://www.lsraudio.com/lvlmeter.html|LSR Audio]] -- incorrect ballistics (overshoot, rise/fall times, jitters at lower freq) * [[http://www.pspaudioware.com/plugins/tools_and_meters/psp_2meters/|PSP Audioware]] -- incorrect frequency response ===== meters.lv2 ===== * IEC 60268-17 / VU * IEC 60268-10 Type I / DIN * IEC 60268-10 Type I / Nordic * IEC 60268-10 Type IIa / BBC * IEC 60268-10 Type IIb / EBU * Stereo Phase Correlation Meter (Needle Display) * EBU R128 Meter with Histogram and History * Digital True-Peak Meter (4x Oversampling) * Goniometer (Stereo Phase Scope) * IEC61260 30-Band Spectrum-Analyzer * Phase/Frequency Wheel * Stereo/Frequency Monitor * DR14 (pleasurizemusic.com, specs by tischmeyer/algorithmix) ===== Look & Feel (1/3)===== {{ :wiki:needle-meters-18.png }} ===== Look & Feel (2/3)===== {{ :blog:meters:lv2ebur128.png }} ===== Look & Feel (3/3)===== {{ :wiki:spectr_and_goni.png?920 }} ===== Real World Testing ===== \\ {{ :pub:av:meters:lac.webm }} ===== Source Code & Documentation ===== * Source-code at [[https://github.com/x42/meters.lv2]] * Licensed under GPLv2 * Binaries available for OSX, GNU/Linux Contributors: * Fons Adriaensen -- DSP-expert (jmeters) * Jaromír Mikeš -- packages for Debian/Ubuntu * Alexandre Prokoudine -- P&R; sponsored book * Chris Goddard and Axel Müller -- testing * Joern Nettingsmeier -- inspiration & motivation ===== References ===== * [[wp>VU_meter]] * [[wp>Peak_programme_meter]] * [[http://www.digido.com/how-to-make-better-recordings-part-2.html|How To Make Better Recordings in the 21st Century - An Integrated Approach to Metering, Monitoring, and Leveling Practices]] by Bob Katz. * "Audio Metering: Measurements, Standards and Practice: Measurements, Standards and Practics", by Eddy Brixen. ISBN: 0240814673 * "Art of Digital Audio", by John Watkinson. ISBN: 0240515870 ===== Part II - Oscilloscope ===== The oscilloscope is the //jack of all trades// of electronic instrumentation tools. It produces a two-dimensional plot of one or more signals as a function of time. {{ :wiki:scope.jpg |}} ===== Requirements ===== For an an oscilloscope to be useful for engineering it must * reproduce the signal (regardless of sampling rate) * be calibrated - both in time and level * allow acquisition of particular events (triggering, signal history) * provide numeric read out An oscilloscope is **not** just a waveform display! ===== xoscope ===== {{ http://xoscope.sourceforge.net/xoscope-1.8.png?550}} Audio support: * OSS * ESD (last update 5 years ago) ===== Signal vs. Waveform ===== {{ https://raw.githubusercontent.com/x42/sisco.lv2/master/img/scopeVSwave.png?800 }} ===== Sisco.lv2 - Simple Scope ===== * classic audio oscilloscope with variable time scale * triggering and buffering * cursors * numeric readout * LV2 plugin format and standalone jack application It is feature complete for an audio-scope but it is rather //simplistic// compared to contemporary hardware oscil loscopes.. ===== Sisco.lv2 - Screenshot ===== {{ https://raw.githubusercontent.com/x42/sisco.lv2/master/img/sisco4.png }} ===== Source Code & Documentation ===== * Source-code at [[https://github.com/x42/meters.lv2]] * Licensed under GPLv2 * Binaries available for OSX, GNU/Linux Thanks to: * Fons Adriaensen -- LAC'13 paper * Jaromír Mikeš -- packages for Debian/Ubuntu * Aurélien Leblond -- video tutorial (w/ingen & AMS) * Damien Zammit -- power user & tester * Tomas Brand -- for insisting on making it scalable ===== The End ===== \\ \\ Thank you for your attention.