Audio vs. File Compression: What to Avoid for Better Audio Quality

It is difficult to represent sound. Most apps display it as a wavelength, but in reality it is a more complex mesh of multiple wavelengths that cover different high and low frequencies. But the process of capturing that sound in a recording, and then sharing it on the Internet, often leads to sounds that are slightly different from what you would experience in the real, natural world around you. One reason is that the audio you are listening to has likely been compressed, which is an editing process to sculpt the sound. The end result can affect how you perceive the soundstage as well as the tenable audio quality you experience. However, if either type of compression is used incorrectly, it can lead to something worse than when you started.

When it comes to music, an audiobook track, or any type of audio paired with visual media, there are ways for artists and editors to ensure that different elements of a recording are heard at the desired volume levels. This is what we call audio compression. Then, when these compositions are delivered to listeners and viewers, compressing the files helps ensure that they sound as good as when they were mastered, but also don’t take up thickets of memory. Those who wear wireless headphones may experience an additional step of compression and decompression compared to most plugged-in users, as the sound travels from the device to its final destination.

In a studio or digital audio workstation (DAW) application like Audacity, FL Studio, or Logic Pro, compressors are used to equalize the perceived loudness of certain sounds: louder sounds are attenuated, thereby bringing out quieter sounds. Apps can control the dynamic range of an entire song or specific adjustable frequency bands, allowing producers to make their cymbals more consistent with other tracks or, for podcast editors, to easily equalize host and guest vocals. Whether it’s a digital plug-in or a physical machine that passes input through amplifiers, vacuum tubes, light bulbs, or transistors, a compressor also gives the sound it affects a certain characteristic evocative of its modulation technique: you’ll hear “warm,” “smooth,” and “creamy” in typical mixer parlance. Vocals in particular can benefit from a decent dose of compression, as they are the element most prone to rapid changes in volume, although they can overexpose breathing and hissing, or sounds like “Z”s or “shhs”.

There are two main levers for compression in a DAW environment: the volume threshold at which compression begins to apply and the ratio or force at which it is applied. At a ratio of 8:1, which is generally considered to be on the border of moderate to loud, a compressor will limit anything above the threshold by a division of 8. So if the input is 16 decibels (dB), it will be reduced to 2 dB. Compression is further affected by attack and release variables, or the times a user sets for the compressor to ramp up and down when it detects an audio signal passing either way through the threshold. The overall process decreases the apparent volume of the affected audio.

A codec (a portmanteau of compression-decompression or encoding-decoding) is responsible for taking the media and reducing it for transport and storage before playing it. With lossless audio codecs such as Free Lossless Audio Codec or FLAC, the file is preserved in such a way that no data is lost during compression and decompression. However, most codecs, including MP3 and Advanced Audio Coding or AAC, are lossy, meaning they compress by removing data using algorithms that focus on less noticeable differences in the sounds in the file. Almost all major music streaming platforms offer lossless and lossy audio quality options for online and offline playback.

Audio streaming, whether a live broadcast or a Bluetooth link between your phone and headphones, also uses codecs to transport audio over bandwidth-limited radio signals between devices, often with an emphasis on low latency. In addition to AAC, parts of the technology industry have developed their own wireless transmission codecs that optimize various aspects, including the power consumption of devices. One such codec is mobile chipmaker Qualcomm’s AptX Adaptive, a widely supported codec that, as its name suggests, dynamically adjusts from fast-response video calls one minute to hi-fi listening the next. That said, in cases where an advanced Bluetooth codec is not available, your equipment can revert to the default sub-band codec (SBC), where quality is limited by a relatively low bitrate limit.