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 Media Filters can have issues with some mp3 audio files produced by third parties, that would play fine if downloaded.consistent user experience across platforms (Mac, PC, Linux) as it plays in the browser.Widest possible compatibility (both software and hardware).Allows longer audio files to play instantly in the browser as they download in the background.Ideal for shorter sound clips which can be flexibly embedded into a document, forums, quizzes, lessons etc.Mono files are another potential cause for audio to playback at twice the expected speed. Full or Real stereo is only necessary for the very highest quality of recording where stereo separation is regarded as important. 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. Mono files theoretically save bandwidth when the location of the audio is irrelevant (e.g. 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. If audio files report that they are much longer or shorter than they really are then VBR incompatibility is a likely cause. 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. 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. 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. 44.1kHz is probably the most compatible and a good default choice but 22 and 11kHz are fairly standard too. Due to something called the Nyquist Theorem you need twice the frequency of the sounds you wish to record. ![]() Sample rate is the number of times per second that the sound is digitally recorded. Somewhere between 32 and 96 kbps is appropriate with diminishing returns beyond 128kbps. The latter is a measure of filesize and download time and also a rough measure of quality. Note that 'sample rate' or frequency, measured in kiloHertz (kHz), is not the same as 'bit rate', measured in kilobits per second (kbps). Joint-Stereo, rather than Mono or Full Stereo.Constant Bit Rate (CBR) rather than Variable Bit Rate (VBR).The short version follows, it is explained in greater depth below: Flash requires the audio to be in a fairly specific format and this happens to also ensure the widest possible compatibility in other situations e.g. The Media Filters in Moodle use Flash to playback audio in the browser. If you are creating audio files, or having them created for you we suggest some specific settings for your MP3 in the next section. It is the most widely used format and is likely to be playable on any modern computer, internet connected device or portable player. If you have a choice in the matter we would suggest choosing MP3. The following formats are widely used and if not already present on a computer, easy to use software can be easily downloaded and installed at no cost. Alternatively, you can try to ensure that the media filter doesn't attempt to process the problematic file. ![]() If this is the case then you may need to follow the Advanced Method outlined below to prepare your audio files for use within Moodle. It can however, in some rare cases cause your MP3 files to sound faster and higher pitched, making normal speech sound like Minnie Mouse, or slower and lower pitched. Turning this on is recommended, and is a job for your Moodle administrator. Moodle has a facility called Multimedia plugins that can make the presentation of some kinds of downloaded audio and video files more streamlined.
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