Sample Rate: only choose either 44.100, 22.050, or 11.025 kHz (lower sample rate as you lower bitrate).Don't tick "Use Variable Rate Encoding".Options -> Advanced -> Importing, then select MP3 Encoder then from Settings: select Custom. ![]() To change the settings used to create or convert audio files, open the iTunes option screen, then select: The following instructions are for iTunes which is freely and easily available for both Mac and PC. 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. ![]() ![]()
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