If you want to transfer music to a laptop, smartphone or other playback device, the question of the right audio format arises. Should it be uncompressed or compressed? The most common audio format is the WAV file, while MP3 is the best-known compressed audio format. But beyond that, there are tons of other audio formats: AIFF, OGG, ACC, FLAC, and others.
In the jungle of audio file formats, it is easy to lose track. Therefore, in this article we would like to give you an overview of which audio formats are available and what the differences are.
What audio formats are there?
Audio formats define the structure of the file in which digital audio data is stored. There are generally two variants: uncompressed audio formats, which contain all audio data, and compressed, which save storage space.
There are two variants of the compressed audio formats. Not all compressed audio formats remove audio data, some just pack it to save space. Accordingly, the compressed audio formats can be divided into lossless and lossy.
All compressed audio formats have in common that they change the structure of the original audio file. They use an encoder that packs the original audio data into the new, compressed file format, and a decoder that reassembles the packed and possibly thinned audio data afterwards so that it can be read and played back by the operating system. Both together – encoder and decoder – are also called codec.
From MP3 to WAV: all common audio formats at a glance
AAC: means “Advanced Audio Coding” and is considered the successor to MP3. AAC compresses more efficiently than MP3, i.e., the files are smaller with the same quality. However, not all players can play AAC files. So, you might need an audio converter.
AIFF: “Audio Interchanged File Format”. This audio format was developed by the Apple company and is the uncompressed standard format on the Mac computer. It roughly corresponds to the WAV format in Microsoft’s PC world.
CDA: These files appear on audio CD tracks. CDA means “Compact Disc Audio”. CDA files do not contain any audio data, but are merely jump markers to the data stream on the CD. The data stream must first be converted into a WAV file before it can be read or edited by the computer. This procedure is called grabbing or ripping.
FLAC: The Free Lossless Audio Codec, FLAC for short, is a freely available, lossless compressed audio format. Lossless means that no signal components are removed and the sound quality is always just as high as with the uncompressed formats.
MP3: is the abbreviation for “MPEG (1 or 2) Audio Layer 3” and is still the best known and most important compressed audio format. MP3 is supported by almost all playback devices and is therefore equally suitable for computers, smartphones, network streaming or portable players. The most important principle: With MP3, only the audible signal components are used and all superfluous data is filtered out.
MP4/M4A: These files use MPEG-4, a method for video and audio data compression. The audio data is losslessly compressed using the ALAC codec, similar to FLAC. In the case of a pure audio file, these files often have the extension “M4A” instead of “MP4”, with the “A” standing for “Audio”.
OGG: is the file extension of the audio format “Ogg Vorbis”. This compressed audio format has characteristics very similar to MP3. OGG is “open source”, which means OGG compression is free and freely available. The downside: not all playback devices can play OGG files or display the metadata about the song, artist, etc.
PCM: Pulse Code Modulation. PCM files contain only the digitized measurements of the analog signal. In order to be able to process such raw data on the computer, they are embedded in so-called container formats such as WAV or AIFF.
WAV: Wave file, the standard format on Windows PC for uncompressed audio. The name “Wave” refers to the waveform used to represent the audio signal.
WMA: stands for “Windows Media Audio” and is a compressed audio format developed by Microsoft. Like OGG, WMA is based on the same principle as MP3. WMA is directly available on all Windows computers, but is not supported by many playback devices.
How do the different audio formats differ?
Uncompressed audio formats
Uncompressed audio formats contain the digital data that results from a digital recording. The electrical signal, which is caused by the microphone membrane, for example, is measured at regular intervals. The intervals of the measurement result in the sampling or scan rate. With an audio CD, this sampling rate is always 44.1 kHz, which means that the signal is measured 44,100 times per second.
In addition to the sampling frequency, the measurement accuracy is important for the sound quality. It is called “sampling depth” or “bit depth”. With the audio CD, this measurement accuracy is fixed at 16 bits. This means that 65536 different values can be displayed. With every digital recording in audio CD quality, 44,100 five-digit numbers are created per second.
PCM files and audio CDs simply contain these measurement data one after the other as a data stream. CDA files, as they appear in the file manager for audio CDs, are merely jump markers that put the CD player at the right place in this data stream. In addition to the measured values, WAV and AIFF files also contain additional information, e.g., on the sample rate, number of channels and other things. Unlike the pure data stream, these files can be read and processed by audio programs on the computer. PCM files and audio CD tracks, on the other hand, must first be converted to WAV files.
Compressed lossless audio formats
In order to save storage space, there is the possibility of tidying up and consolidating the data stream. For example, there is no need to store the same number many thousands of times over the entire period of time when nothing at all – silence – is measured. Rather, it is sufficient if the required period of time is specified and a single measured value is saved. In this way, the amount of data can be reduced so that the original data stream can later be reconstructed without loss.
This is the basic principle behind compressed, lossless audio formats such as FLAC or ALAC. The original files become significantly smaller without losing any information. Compressed lossless audio formats will therefore always sound exactly the same as the original recording.
Compressed lossy audio formats
However, the original files cannot be reduced arbitrarily in this way, but only to around 50%. If that’s not enough, i.e., if you want to fit more audio on the data carrier, you have to resort to a lossy compressed audio format.
But the losses with MP3, OGG and Co. are more of a theoretical nature. If you set the encoder bitrate generously, you won’t hear any difference, but you’ll get about 1/10 of the original size. So, you can pack at least five times more music onto your player than with a lossless format.
Roughly speaking, the way it works is that inaudible or double measured values are filtered out of the data stream. Many tests were made for this method to determine what humans can hear and what not. On this basis, the Fraunhofer Institute – the inventor of MP3 – then developed a psychoacoustic model that can be used to separate the audible from the inaudible signal components – that was the birth of MP3.
Besides MP3, there are many other compressed lossy audio formats. OGG is a freely accessible format for which no license fees are due. WMA is a variant of Windows. With AAC, a further development has emerged that compresses even more effectively.
Overview of audio formats
Table with audio format name, compression type and file extension
Which audio format is suitable for which purpose?
Which audio format should you choose? It depends what is important to you. If you care about sound quality and storage space, then WAV is your best bet. Because WAV is supported by almost all devices. That means: You can play WAV files anywhere or pass them on without any problems.
If you know the playback device and want to store as much music as possible on it in the best possible quality, then it is best to use a compressed lossless audio format such as FLAC or ALAC. This saves you about half the storage space, so you can accommodate twice the amount of music. In addition, the metadata – i.e., information about the title, artist, etc. – can be displayed, which is not possible with WAV or only with difficulty. However, you should first check whether the playback device supports this format. Also pay attention to the metadata – often the FLAC file is played, but the track information is not shown on the display of the device.
If small file size, metadata, sound quality and broad device compatibility are equally important to you, MP3 is still your best choice. MP3 is the all-rounder, so to speak. Don’t worry that the sound might be somehow worse than WAV, FLAC or AAC – if you set the MP3 encoder to 128 kbit or higher, you won’t hear any difference from the original even under professional headphones. The benefit of AAC would be that you get even smaller files than MP3 without sacrificing sound quality.
Conclusion: Ultimately, the playback device decides. Not all devices can play WMA, M4A, OGG, AAC or FLAC. Some devices play such audio formats, but do not display the metadata. You are still on the safe side with the comparatively old but still good audio format MP3.
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