Post by: Audio Engineer – Matt Bishop
It wasn’t all that long ago that audio on show site was an entirely analog affair. Playback and record were handled on archaic devices like cassette decks or reel-to-reel machines. Today there are all kinds of digital audio devices. Computers, CD players, solid-state recorders, Instant Replays, multi-track systems, and the list goes on and on. The progression of digital technology has also yielded a wide variety of formats that can leave you with as many questions as you have options. The average person doesn’t have to worry about all of this beyond selecting settings in iTunes, but production professionals are consistently dealing with audio files ranging from low-fi MP3’s to massive, high-resolution WAV files. A regularly asked question is “what’s the best file format to use on shows?” We’ll give you some information and suggestions that will hopefully bring clarity to both the discussion and the audio on your next show.
Digital audio can be broadly broken down into two categories, compressed and uncompressed formats. Both categories have a variety of sample rates and bit depth options, the combination of which determine the maximum potential quality of the file. I’m sure you are now wondering, “what is sample rate and bit depth?” I’ll try to explain. Think of sample rate as the number of slices contained in each second of audio and the bit depth is the number of chunks contained in each slice. The bit rate is determined by multiplying the sample rate by the bit depth but is generally expressed as the equation sample rate/bit depth (i.e. 44.1Khz/16 bit which winds up being 1,441.2kbps when multiplied by 2 to account for it being stereo). As you might have guessed, the higher the bit rate the better things should sound.
A common example of uncompressed audio is a compact disc, which contains 44.1 Khz/16bit uncompressed files. Professional digital recordings would also be captured in an uncompressed format such as a WAV/Broadcast WAV (waveform audio file format) or AIFF (audio interchange file format). The WAV and AIFF file formats sound and perform identically, the only difference is how the information is stored on the disc. Uncompressed audio can be recorded at different sample rates as high as 192khz with bit depths as high as 24 or 32 bit. Naturally, uncompressed audio exhibits superior sonic qualities. Uncompressed audio also takes up a lot of digital space (the higher the bit rate, the more data that is being written to the disc). For the sake of comparison, a stereo 44.1/16 file like found on a CD takes up 10.3 MB per minute of material and a 192/24 file would take 67.5 MB per minute. This is generally information that doesn’t make a difference to anyone other than the audio guy but it’s good background info for the conversation.
With the advent of file sharing on the web it became necessary to create compression algorithms for audio (it was taking way too long for people to steal music!). While not alone, the most common compression codec today is MP3. Typically MP3’s have a sample rate of 44.1khz but that is rarely referred to. MP3 quality in generally referred to by its computed bit rate (kbps) with common bit rates falling between 128 and 320kbps. So if the audio from a CD is converted to 128 kbps it is being compressed at a ratio of approximately 11:1 while a 320 kbps MP3 is compressed at around 4.5:1. The result of compression is lower quality sound but much smaller file sizes. For example, 320 kbps MP3 only consumes 2.3 MB per minute of stereo material.
With the advent of iTunes, Apple introduced a proprietary compression codec called Advanced Audio Encoding, commonly known as AAC. Originally these files were 128kbps with file sharing protection, but the more recent iTunes plus format has changed to a 256kbps bit rate without file protection. AAC files use the following file extensions .aac, .m4a and m4p for protected files. It should be noted that protected AAC files (.m4p) will only play on computers with an authorized iTunes account. A common problem on shows is getting a jump drive full of protected iTunes files. Since only an authorized computer can play those files, whomever the files came from ends up having to go back and burn the tracks to a disc. iTunes software will play MP3, WAV and AIFF file formats; however any song downloaded from iTunes will be an AAC file.
Although the creation of Napster, iTunes and other online music services has lead to almost universal acceptance of compressed audio, there are still questions about the quality of compressed audio. Lower bit rate mp3 files lack fidelity in the low end and also tend to sound harsh and garbled in the top end. Although the quality is not great, the small file size makes low resolution MP3’s very valuable when recordings have to be sent electronically. On the other hand, higher bit rate compressed audio can be used in virtually any show site application where you would use uncompressed audio. Listening on a PA system, you would be hard pressed to discern the difference between a 256-320kbps MP3 file and a standard CD. The combination of fidelity, compact file size and compatibility makes high resolution MP3’s a perfect format for use on shows.
There are a few other file formats that may also be encountered on a show. Lossless compression formats such as FLAC (Free Lossless Audio Codec) and Apple Lossless maintain virtually identical sound quality to their uncompressed counterpart while cutting the file size in half (approximately). While these file formats perform as advertised, the lack of compatibility across different platforms makes them far less useful on a show than either MP3 or uncompressed files. Microsoft’s Windows Media Audio or WMA is a less venerable format but does show up on site from time to time. These seem to most commonly come from end clients who are providing a song they want played or something like that. These formats can be easily converted to MP3 or WAV with iTunes or other conversion programs.
So the question remains, what file format is best for shows? The answer is……it depends. For music that is going to be used in a show, the best options are WAV files or a 256kbps or greater MP3’s. While the AAC’s and AIFF’s are great, the universality of MP3 and WAV makes them easier formats to deal with on show site. Most every playback and editing program will accept both MP3 or WAV making playback and manipulation a snap. Digital files are also easy to transfer. Transferring files from a hard disc or thumb drive is fast and it retains all the folders and labeling making file identification much easier. For most engineers this is the preferred method of receiving files, even over CD’s. For recording shows, it once again depends on what you’re planning to do with it. If you’re just recording spoken word and need to distribute the files electronically, 128 kbps is a perfect compromise between quality and file size. For quality recordings using a higher bit rate MP3 (256-320 kbps) or WAV file is always a safe bet.
As you can see, audio is no longer as simple as pushing play. With different file formats, bit rates and a multitude of playback and recording platforms there are a ton of options. However, the flexibility and power of this medium has given us the capability to use audio in new and exciting ways while also improving the basic functions of sound.
Our Audio Department is here to help you decide which formats will work best for your show and we can make sure that everything sounds just right. Just call (972-538-9400) or e-mail John Caswell, our Manager of Audio Services, and he’ll be happy to help choose the right format for your next event.
