Audio File Formats
In the 10 past years working for production music companies and recording studios there has only been a small handful of audio file formats that I have needed to know about and work with. There are dozens and dozens of available audio file formats but there is absolutely no need to know all of them. The most important things to know about digital audio formats are the following:
- Difference between analog and digital (explained in previous article).
- Difference between a compressed format and non compressed format.
- Short listing of actual formats, what software uses them, and what they are good for.
The funny thing with audio file formats is that just about all the formats are geared for either PC or Mac computers. Though lately in the past 5 to 7 years they have gotten explosively cross compatible. So each file type has a home and origin from a particular platform (PC or Mac). But almost all the popular software now plays almost every popular file type. In short we will be discussing these formats; WAV (.wav), AIF(.aif or .aiff), PCM(.wav or .aif), MP3(.mp3), WMA(.wma), OGG(.ogg), MPEG-4(.mp4 or m4a), and AAC(.aac).
The simplest format to discuss are non-compressed formats. Non-compressed formats basically capture the sound at the indicated rate of your equipment with no extra processing. What I mean is if you are recording with a digital piece of equipment, some where in the setup of that equipment you can indicate what format or resolution you can record at. These resolutions will be illustrated in kilohertz and bytes like this 44.1khz/16bit which is standard CD quality. There are devices that will record better than CD quality and you can see resolutions like 96khz/24bit. Basically the higher the number the better the quality.
The most popular of these non-compressed formats are WAV and AIF. WAV files are a PC based file format and sometimes are called broadcast WAV file. AIF (or AIFF) is a MAC based file format. So if you are working on a MAC, yes your software can play WAV files, but I would always recommend using the file format that is native to your system. You will incur less issues down the road. Same thing applies to PC’s, when all possible stick to WAV files. These formats offer the most resolution compatibilities than any other format. If you are a professional and quality is important to you these are the formats you need to be using.
Now from time to time you will hear a format called PCM. This is a little strange in that the file extension does not end in ‘pcm’. PCM more or less means that the file is in a header-less non-compressed format. This can be in either WAV or AIF format.
Moving to Compressed formats that should, in theory, be the next in line for best quality. These formats are MPEG-4 and WMA which utilize a ‘lossless’ compression algorithms. Naturally these formats also have origins to particular platforms. MPEG-4 has it origins with MAC, and WMA is for PC. WMA stands for windows media audio. The concept of this compression format is to compress the file as much as possible, BUT without diminishing quality. The funny thing about these compressed formats is that they are not the popular ones. They are very proprietary and through history never really were cross platform friendly, which in my opinion is one of the main reason they are not used more today. The funny thing is that I have used these formats SO little, that I can’t even get into the resolutions they support. The important thing to remember for this compression type is quality is priority.
The last format is the most popular at the time for the general public at the consumer level. This is the ‘lossy’ compression formats of MP3 and AAC. MP3 is mostly PC based and AAC is the MAC particularly Itunes format. These formats do not focus on quality, rather than reduce quality in order to achieve the desired file size. The resolution of these files are measured in kilobytes per second or ‘kbps’. What exploded these audio file types to super status is the ability to obtain ‘near’ CD quality with an average of 1/10th the file size. So an average 40mb wav file can be compressed to 4mb and will sound just as good to the standard consumer user.
To take lossy compression one step further, there is two methods of this compression. They are CBR and VBR which are constant bit rate and variable bit rate. CBR is the most used and my recommended rate. It offers consistency and seems to be the most reliable amongst all players. Reliability is the key for this format when it comes to small mp3 players and Ipods. It is my feeling VBR is used to imitate the nature of lossloss compression and actually compressed to regards of quality. But be warned, eventually VBR has caused me problems.
So what are the best resolutions to use for MP3 and AAC? Depends on your use. If you want great consumer level quality you will want to compress as Itunes does, which is 256kbps or one step up to 320kbps. No need to go any higher. In my opinion 256kbps sounds awesome and most will never ever tell the difference. It’s even difficult for me to tell. I have personally found that you can go as low as 192kbps and still get great quality. Once you get below 160′s then you start hearing things that any consumer user can detect. So what is it that they are detecting? First to go is the high and low frequencies. The high’s won’t be as crisp or defined. The low frequencies will not be as round, hard hitting, and also defined. After that then the entire frequency spectrum gets diminished.
The interesting thing with MP3 and AAC, is that they are private or proprietary formats. Which means the persons or company that own these patents and compression formats have total control and any software that utilizes these formats to create audio files has to get permission and pay for the right to do so. With the internet and open source methodology growing vastly a new file format has become popular in a small way is OGG. OGG is a lossy compression type and it is open source. Which means it is free to use, share, modify, and improve. But I will say that, I have never encountered this file format in my professional experience. Only once in a blue running across it on the internet and hearing of its popularity. I will always stick with WAV, AIF, MP3, and AAC.
Below is a music file that I have originally created in WAV file. This is the file sizes compressing it to other formats.
Song Length: 3:36
WAV (44.1khz/16bit)- 36.4 MB
AIF – (44.1khz/16bit)- 36.4 MB
WMA- (256kbps)- 6.65 MB (still at 44.1khz/16bit)
MPEG-4- (254kbps)- 6.58 MB (still at 44.1khz/16bit)
MP3 (256kbps)- 6.6 MB (still at 44.1khz/16bit)
AAC (256kbps)- 6.6 MB (still at 44.1khz/16bit)
So these are just file size comparison. You can do your own test and check for actual quality. Either PC vs MAC file format are no difference in size. I hope this helps your understanding of audio file formats!