Lossy audio formats

MP3, AAC and other standard lossy audio formats

Who would have thought it, but just like Teufel loudspeakers, the MP3 audio format comes from Germany. Work on this now-famous codec began in the 1980s at the the Fraunhofer Institute, a research organization in Erlangen, Germany and in 1996, a United States patent was issued to the institute for the MP3. The explosion of the internet in the late 90s came at the perfect time for the little audio format: The MP3’s ability to reduce the size of a digital music file by one tenth was a huge benefit when it came to sharing digital music. In the days before broadband, it allowed music to be down- and uploaded  in a matter of minutes. Now, nearly 30 years on, the MP3 is synonymous with digital music files.

Lossy versus lossless audio

Digital audio formats like the MP3 can be divided into two main categories: Lossy and lossless. Lossy formats are those that permanently remove part of the original digital file in order to create a smaller version that’s easier to transmit and store. This was especially critical in the early days of MP3 players when storage space was at a premium. Whereas a typical 3 minute pop song on a CD takes up approximately 30 MB of space, the same song compressed as an MP3 is only 3 MB. Other lossy formats like AAC (also known as the MP4), OGG and WMA also are also lossly digital music formats that compress music by reducing data in order to create smaller files.

Teufel’s AIRY Bluetooth headphones use the aptX codec to transmit CD-like sound quality.

At first glance, it would appear that an MP3 compressed to such a small file size would be incredibly compromised in terms of sound quality. However, clever use of perceptual audio coding developed by the Fraunhofer Institute takes advantage of the limits of human hearing such as the fact that most people – depending on age – have a diminished ability to perceive sounds over 16,000 Hertz as well as everything under 20 Hertz. This is known as reducing the redundancies in an audio file; that is, the elimination of recurring elements that add nothing to the overall sound. In addition to taking advantage of the physical limits of our eardrums, lossy codecs make use of our brains’ limited ability to take in and process all of the information contained in sound. A process known as psychoacoustics helps locate these imperceptible sonic elements from a sound track for removal. The discarding of sounds that we most likely will not perceive is an example of how perceptual coding targets irrelevancy. Along with the removal of redundancies, the targeting and removal of irrelevancies is a key tool used by MP3s to create a smaller file size. This is effectively achieved by reducing the bit depth of the part of the audio file that is deemed irrelevant or redundant such as very soft parts masked by much louder sections.

Sound quality

As rational as the process of lossy audio compression sounds, many feel that the resulting sound is inferior to the original, which is usually an uncompressed 16 bit 44.1 kHz CD quality digital file. Lossy files are felt to produce a sort of “ear fatigue” whereby the act of listening to music quickly loses its appeal and becomes boring or irritating, a phenomenon likely due to the lack of adequate nuance in the sound. It may not seem rational that we can miss what we don’t hear, but many argue that just because a sound isn’t consciously heard doesn’t mean that it isn’t subconsciously perceived or that the overall tonal quality is not somehow coloured by it. This realization quickly led to the adoption of other digital audio formats that promised better sound quality. By the time the first incarnation of the music service Napster shut down in 2001, downloadable music had already become an established part of the music world and was quickly followed by a range of legal download opportunities such as Apple’s iTunes Store which offered a next-generation digital file called AAC for Advanced Audio Coding.

AAC files are the same size as MP3s but offer better sound quality, and while the Californian computer giant did not develop the AAC format, it helped establish its popularity. While Apple supports the MP3 format, it also offers the opportunity to convert these files into AACs. Of course, with either file, the bitrate rate, measured in kilobits per second, is also a deciding factor when it comes to sound quality as these can vary, even within a single format. The higher the bitrate, the better and more natural the sound will generally be. To provide some idea of what the bitrates signify, talk radio is about 56 kbps – decent but not good enough for music playback which is usually starts at 96 kbps. Most AAC files today have a bitrate of 192 – 224 kbps. The iTunes Store even offers 256 kpbs. This renders very high quality music playback, at least when it comes to lossy digital files.

Lossless audio formats

Those who want to enjoy digital music in the highest possible sound quality but who don’t have the storage space for uncompressed files (such as WAV) are likely to use audio files that employ methods of lossless compression. The most popular formats are Apple’s ALAC (Apple Lossless Audio Codec) and FLAC (Free Lossless Audio Codec). Lossless compression uses a method of compression that does not permanently delete any of information from the original digital source file, in most cases a CD. The tradeoff is size. A FLAC or ALAC file will have anywhere between 50 – 60% of the original file size. In the case of a 3 minute pop song, this means a file size of about 15 MB as opposed to just 3 MB for an MP3.

Although Apple has developed its own lossless audio format, music in this form cannot yet be purchased from its iTunes store. Rumor has it, however that this is planned. In the meantime, it’s felt that 256 kbps AAC format music files offer a quality that is perfectly satisfactory for most music fans. Those who would like to purchase lossless files can do so from other sources. Even some streaming services such as TIDAL now make lossless music files available. The FLAC codec is often used as it can be decoded with relatively little processing power.

Coda: The audio format that made music truly shareable

Even if the MP3 format has been surpassed by other codecs in terms of sound quality, it remains synonymous with digital music files. And how could it be otherwise? After all, the MP3 was the first technology that allowed music to be copied and shared on the internet. Today, next generation codecs such as AAC have largely surpassed the MP3. While many are still lossy, they offer a better sound quality than MP3 while retaining the ability to radically shrink file sizes for better transmission and storage. Increasingly, however, true music enthusiasts look to lossless audio formats like FLAC and ALAC for CD quality audio. Broadband internet and more affordable storage systems have dropped the barriers to streaming and storing these larger files, fueling their popularity.

All pictures: Property of Teufel Audio

MP3, AAC and other standard lossy audio formats
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