Audio avanzado

Saltar a: navegación, buscar

Nota: Pendiente de Traducir. ¡Anímese a traducir esta página!.     ( y otras páginas pendientes)

  • Esta es una página de solución de problemas acerca de como crear archivos de audio y usarlos para el mejor efecto en Moodle.
  • Para las instrucciones básicas acerca de como añadir sonido a su curso Moodle, vea Audio.

Filtros multimedia

Moodle tiene una opción llamada Filtro de plugins multimedia que puede hacer más ágil la presentación de algunos tipos de archivos descargables de audio y video. Se recomienda activarla, y es un trabajo para su administrador de Moodle. Esta característica puede, sin embargo, en raras ocasiones hacer que sus archivos MP3 suene más rápido y en tono más agudo, haciendo que el habla normal suene como Alvin y las ardillitas, o más lenta y grave.

Métodos Avanzados

LOs filtros de medios en Moodle usan Flash para reproducir audio en su navegador. Flash requiere que el audio esté en un formato bastante específicoy esto sucede también para asegurar el rango más amplio de compatibilidad en otras situaciones, como por ejemplo al reproducirse en un iPod. A continuación explicamos la versión corta, y más abajo está la versión más detallada:

  • formato MP3
  • con una tasa de muestreo de 11.025, 22.05 o 44.1 kHz
  • Tasa de Bit Constante ( Constant Bit Rate (CBR)( en lugar de variable (VBR)
  • Estereo unido ( Joint-Stereo ) en lugar de Mono o Estereo Completo ( Full Stereo )

Note that 'sample rate' or frequency, measured in kiloHertz (kHz), is not the same as 'bit rate', measured in kilobits per second (kbps). The latter is a measure of filesize and download time and also a rough measure of quality. Somewhere between 32 and 96 kbps is appropriate with diminishing returns beyond 128kbps.

Sample rate is the number of times per second that the sound is digitally recorded. Due to something called the Nyquist Theorem you need twice the frequency of the sounds you wish to record. 44.1kHz is probably the most compatible and a good default choice but 22 and 11kHz are fairly standard too. You might sometimes find MP3 audio files at 16, 32 and 48 kHz but these can cause problems with Moodle and elsewhere and so ideally should be re-encoded following the instructions given below.

Variable Bit Rate files are commonly used to get the best audio quality by 'saving up' bit on easily encoded sections such as silence or simple audio and then using them for difficult to encode noises such as applause, harpsichords or hi-hats. Constant Bit Rate mp3s can be seen therefore as wasteful as they use the same amount of bits for silence as they do for a full orchestra crescendo but are more compatible and easier to stream. If audio files report that they are much longer or shorter than they really are then VBR incompatibility is a likely cause. If audio sound faster or slower than it should, an you have ruled out the sample rate as a cause then VBR may be the culprit.

Mono files theoretically save bandwidth when the location of the audio is irrelevant (e.g. a single person talking), but joint-stereo mp3s can encode most stereo info with minimal quality loss and are smart enough to deal with primarily mono audio without wasting bits and unnecessarily increasing filesize and download time. Full or Real stereo is only necessary for the very highest quality of recording where stereo separation is regarded as important. Mono files are another potential cause for audio to playback at twice the expected speed.

Pros

  • Ideal for shorter sound clips which can be flexibly embedded into a document, forums, quizzes, lessons etc.
  • Allows longer audio files to play instantly in the browser as they download in the background.
  • Widest possible compatibility (both software and hardware)
  • consistent user experience across platforms (Mac, PC, Linux) as it plays in the browser

Contras

  • Can require more preparation
  • The Media Filters can have issues with some mp3 audio files produced by third parties, that would play fine if downloaded

Conversión a MP3 compatible

If you have audio in one of the other formats listed above but would prefer it in the widely compatible MP3 format detailed above then most can be easily be converted. The following instructions are for iTunes which is freely and easily available for both Mac and PC.

To change the settings used to create or convert audio files, open the iTunes option screen, then select:

Options -> Advanced -> Importing, then select MP3 Encoder then from Settings: select Custom...

  • Stereo Bit Rate: your choice. (see below for guidance)
  • Don't tick "Use Variable Rate Encoding"
  • Sample Rate: only choose either 44.100, 22.050, or 11.025 kHz (lower sample rate as you lower bitrate)
  • Channels: Stereo
  • Stereo Mode: Joint Stereo
  • Don't Tick "Smart Encoding Adjustments" (this doesn't have any effect unless you have left some settings at 'auto')
  • Tick "Filter frequencies Below 10 Hz" (this generally doesn't have any effect but doesn't really hurt and can increase quality)

If you have played the file in iTunes you should be able to find it in your library. After selecting the file you should find an option in the Advanced menu, called Convert Selection to MP3. If you have several files to convert you can select them all at the same time.


Elección del bitrate

If you already have an existing file then you shouldn't change the bitrate without good reason. It is the equivalent of photocopying a photocopy and each copy introduces degradation and artifacts. If you're not going to reduce the bitrate by 50% or more you would probably be best leaving it as it is.

MP3 bitrates can range from 1 to 320kbps. You can experiment to find the right mix of size and quality appropriate for your content but anything over 128 kbps is probably a waste of time and space for anything other than recording high-quality music, as is anything higher than the bitrate you start with if converting from one format to another. From 32 to 96 kbps is roughly the right area for recording speech.

Módulos y programas de audio

Please see the complete list under See also. The information in this page maybe moved to their own pages in the future.

Usando Audacity para convertir audio y grabar voz

Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems. Learn more about Audacity... Also check our Wiki and Forum for more information.

  • Note: Audacity may not be suitable for encoding MP3s for use with Flash Player at the default sample rate settings. At lower bit rates, it uses sample rates that are not a multiple of 11.025 kHz and the resulting MP3 files may either play at an incorrect speed, the chipmunk effect, or not play at all. See the Audacity documentation on how to set the sample rates.

Características

Interfaz de Audacity
  • Grabar audio en vivo.
  • Convertir cintas y discos a grabaciones digitales o CDs.
  • Editar archivos de audio Ogg Vorbis, MP3, WAV o AIFF.
  • Cortar, copiar, juntar o mezclar sonidos.
  • Cambiar la velocidad o el tono de una grabación.
  • ¡ Y más! Vea la lista completa de características en idioma inglés.


Ayuda y tutorial de Audacity

Vea también

MoodleDoc Links: