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No. 201 February 2021


Images: press materials
Translation: Marek Dyba

No 201

February 1, 2021

How streaming services changed the way audio engineers think about mastering and what comes out of it

STREAMING SERVICES have changed consumers habits for good. Less and less music will be purchased on physical carriers, and the sale of files will also almost completely disappear - only services where, for a relatively low fee, you will be able to listen to millions of albums, will remain. Like every revolution, this one also has a PRICE.

OR MANY YEARS, from the moment COLUMBIA introduced the LP (Long Play) format in 1948 until the introduction of the first Compact Disc in 1982, there was a kind of "standard" for mastering LPs. By MASTERING I would understand all the activities of a sound engineer and producer, whose task is to extract the best features from the stereo mix, unify them, arrange the recordings in order, choose the breaks between them and determine the average level.

⸤ As early as 2010, Apple Music implemented the "Mastered for iTunes" program, which was designed to improve the sound quality in this service of a music signal with too low dynamics, often distorted; On August 7, 2019, the name was changed to APPLE DIGITAL MASTERS | photo:

It was not an actual standard, as no guidelines were adopted by any of the organizations, yet it was known how the material should be prepared. Similarly, there was a common, adopted way of how to change such a MASTER while preparing a production tape intended for pressing an LP record - then a PRODUCTION MASTER was created. The advent of Compact Cassette tapes did not change that, and far-reaching changes were forced only by the first consumer digital format - the Compact Disc.


The point was that a completely different maximum signal level had to be adopted - it could not exceed 0 dB - as well as its average level. On the other hand, there was no problem with the production line, because the master in question was used directly for pressing the discs. After some time, mastering engineers got used to the new medium and began to prepare their masters for it - first in 16/44.1 resolution, then in 20/44.1, and finally they moved to 24-bit high definition recordings.

The only element they had to deal with was the need to shorten a word from the 20 and 24 bits to the 16 required by the CD format. But it also became irrelevant as soon as we started playing files from computers, and later using file players, and finally when streaming became popular. The mastering engineer simply prepares a 24-bit PCM file, sometimes a DSD one, with the selected sampling rate, which is later converted in one of the programs to the 16/44.1 for CDs or an LP is cut from it (without changes).

⸤ YouTube is currently the largest music site | photo:

So it would be a classic story about switching from one format to another, with a happy ending in which the maximum advantages of the digital signal were used. It's just that where there is money involved, human habits and the market, such linear progress does not apply. You can talk about some local progress at most, in a small section of the market, that often later is withdrawn.. This is also the case with mastering today.


With the advent of legal sources of digital files, and it was primarily Apple's iTunes service, the engineer preparing the master disc had to take into account the environment in which the material would be transmitted and played, especially compression. The AAC system, i.e. Advance Audio Coding, used by Apple from 2003, assumes the highest bitrate at the level of 256 kb/s, which is significantly lower than a CD, not to mention hi-res files. For this to work, the signal must be properly prepared. When using a codec, an audio engineer uses three different techniques to reduce its volume.

The first is known as "perceptually irrelevant signal" and involves throwing out from the signal sounds that are "masked" by others that are close on the frequency axis and louder. The second is to reduce bit rate, known as "spectral band replication". Here, the amount of treble and bass is simply lowered, thus reducing the amount of information. When played, they are "recovered" based on information from the lower ranges. And finally, there is the technique of reducing stereophony - at the lowest bit rates the signal is almost monophonic.

The popularization of digital signal transmission in FLAC files solved all these problems. Or at least it should have. Mastering engineers very quickly had to accept the obvious, namely that the vast majority of music would be sold via streaming services or would be disseminated free of charge via YouTube - as reported by research centers, the value of music sold in 2020 this year way surpassed all other sales channels, including physical media and sold files. And that changes the rules of the game.

⸤ Morningdew Media portal and tips on how to prepare a SPOTIFY master |

The problem is that streaming services are sort of independent "kingdoms". There is no common format for streaming. Therefore, each of the biggest players, i.e. iTunes, YouTube, SoundCloud, Dezeer, Spotify and Tidal, does it their own way, without thinking about what other do.

One of the basic tools they use is loudness optimization. The idea is that the individual songs played from different albums are perceived as they have the same volume level so that the user does not have to constantly adjust the volume. In Apple Music, Spotify and Tidal you can turn this feature off, but hardly anyone knows about it. There is no "problem" with YouTube because it cannot be done and normalization is on all the time.

It's a complicated process that works differently on an audio signal, even within a single track. Therefore, mastering engineers working for large studios began to prepare the material already at the mastering stage, so that the optimization function worked as well as possible during streaming, at the same time departing from the objectively best sound. What's more, in the case of YouTube, the optimization of the file takes place in stages and can be completed only after a few days from its "upload", so there is no way to check it.

Optimization is a necessary evil, but for most people it is actually a useful feature. Unfortunately, it can be done in a wrong way. An experienced engineer knows that optimization works from a certain signal level, not for the entire duration of the track, so it “adjusts” the dynamics of the song so that equalization (ie compression) is “turned on” as little as possible. To do this, however, it must use the right level meters - and these are not UV meters, as in classic audio recorders, but LUFS meters.

LUFS stands for "Loudness Units Full Scale". It is a normalized sound loudness measurement that takes into account both human sound perception and the intensity of an electrical signal. LUFS meters are used to determine the standard levels in audio systems for cinema, TV, radio and music broadcasts.

⸤ Screenshot of Izotope Insight |

Do you remember the so-called "Loudness war"? - Let me remind you that this is a tragic (for the sound quality) competition between - first - radio broadcasters and then music labels, based on compressing the signal as much as possible so that it sounds louder than the competition's material. The result of these manipulations was a loud, but at the same time lifeless, with almost no dynamics, bright and screaming sound. Many albums from the 90s and 2000s sound like this. The optimization we are talking about in the context of streaming is a much more subtle and sophisticated process, but it is the same: deviating from perfect sound for the sake of sound adapted for streaming services.

Mastering engineers began to control (censor) themselves and make sure that their master was ready for streaming. So - manipulated. So one should know that even if we get a hi-res file in MQA, WAV, FLAC, etc., it is already pre-prepared for streaming. Moreover, the same master is used for CD and LP production. So in many cases we get a semi-finished product without even knowing it. It's just that the "we", mentioned in the previous sentence, applies to the small percentage of music listeners, that is us, audiophiles. Everyone else will get - paradoxically - a better product, because it is adapted to the medium they use.

Because you don’t really think that the engineers mastering the material for a new album will prepare a separate one for physical media and for sale in the form of hi-res files, do you? They will do what the market requires of them, that is, they will adapt. And this customization will be a step back. So you may have to wait for the trend of remastering the material from "streaming times" aimed at reversing of all this processing. Or maybe I'm just naive and nobody cares, and the decade that is just beginning will be the first period in the history of phonography in which STUDIO MASTER will be deliberately worse than it would be if the rules of art were followed...



  • JACOB GANZ, What 'Mastered For iTunes' Really Means, 5.03.2012, accessed: 23.12.2020
  • JOE ALBANO, What Every Producer Needs To Know About Meters When Mixing & Mastering, 25.06.2020, accessed: 23.12.2020
  • JON SCHORAH & SAM INGLIS Mastering For Streaming Services, 06.2017, accessed: 23.12.2020
  • MATTIAS HOLMGREN, Mastering for Spotify LUFS – How to prepare a master for Spotify?, 22.09.2018, accessed: 23.12.2020
  • IAN STEWART, Mastering for Streaming Platforms: 3 Myths Demystified, 24.10.2019, accessed: 23.12.2020

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