SoundCloud Sound Quality Study

In 2014, I conducted a detailed study of the quality of sound on YouTube (the material is still very relevant, major changes on YouTube during this time did not happen), shortly before that I checked how well the music is played on the social network VKontakte. In the same article, I explore the quality of sound on a service designed exclusively for music - SoundCloud .

But first, a brief historical background:

SoundCloud started back in 2008 as a service for publishing and sharing musical compositions. Initially, it was intended for musicians, who now have the opportunity to conveniently share their sound recordings and publish them. Service is rapidly gaining popularity: in 2010, the number of users reached one million, and in 2013 it exceeded 40 million (with the number of listeners per month exceeding 170 million). However, SoundCloud continued to be solely a way for musicians to distribute their own music, and it was impossible to download music that was protected by copyright. Negotiations with music companies for a long time were unsuccessful. In 2014, we were able to conclude an agreement with the Warner Music Group, but the labels reacted skeptically to SoundCloud. Only in 2016, SoundCloud finally established cooperation with the other two members of the Big Three - Universal Music Group and Sony Music Entertainment, which made it possible to increase the amount of available content to more than 150 million tracks and launch the SoundCloud Go music service (at the moment available in the USA, Canada, France, Germany, the Netherlands, the UK, Australia and New Zealand), allowing you to listen to licensed content.

So, in recent years, the global desire in the IT sphere to simplify everything has led, among other things, to the fact that people have simply become lazy to download music from trackers, file exchangers, etc. (everyone has already forgotten about buying discs) It is easier to drive the name of the track into the search for VK, YouTube, Yandex.Music, etc., press the Play button and do not worry about anything else.

But since each music service has its own troubles with regards to copyright, paid / free content, restrictions, and so on. (Alas, the time has passed when VK was everything and for free), the number of alternatives continues to grow. One of these alternatives is SoundCloud, whose proprietary features are displaying the progress bar of the track as a stylized waveform, the ability to add comments with reference to time, as well as the ability to embed tracks on Twitter, Facebook and generally any pages (using the API).

I have never used SoundCloud before, but recently they sent me a link to a good mix that was posted on YouTube. I looked at the list of formats available for download, found Opus there and was already going to download / listen, but then I noticed in the description a link to SoundCloud - supposedly the mix was initially laid out there. I decided that it was better, as they say, to refer to the original source, and clicked on the link.

Clicking on the Download button, courtesy of SaveFrom.net plugin (which, by the way, I use for YouTube), I downloaded the first track - unfortunately, turned out to be 128 kbps MP3 - and compared it with Opus downloaded from YouTube:

Spectrograms differ a lot - Opus has a wider spectrum, and this suggests that a downloaded 128-kbit MP3 is not a primary source.

But where, then, is the source? Is it available for download at all? Google, for example, has Takeout , which allows you to download originals uploaded to your Youtube video channel (see my article).

I registered on SoundCloud and unloaded the RightMark Audio Analyzer test signal in FLAC format 24 bit / 96 kHz:

By the way, PCM, FLAC, ALAC, OGG (Vorbis, Opus), MP3, AAC, and WMA are available for download from HQ formats (AMR and MP2 are not taken into account) - the lack of additional lossless formats (Monkey Audio, WavPack) is somewhat distressing.

After unloading, I downloaded the track with the same button - I also downloaded MP3 128 kbps. I checked and found out that this is exactly the material that is played streaming when you start playing. By the way, it is better to still play it, after downloading and running, for example, in foobar2000 (provided the settings are correct ) - so you will insure yourself against additional quantization noise (browser decodes to 16-bit PCM, foobar2000 - to 32-bit float ) and clipping (musicians recommend normalizing tracks to -3dBFS before laying out on SC, but not everyone does it).

I also found out that SC converts absolutely everything - even if you download the encoded MP3 to it, it will still encode it again.

Digging on the Internet, I found out that in order to be able to download the original of my track, you must have a Pro account. But, as it turned out, you can still download the original - for this you need to enable the ability to download the track in the Permissions section. Then downloading the original becomes available to everyone, including the owner:

This can be done for both private and public records.

Well, it already pleases. But the service has very few records for which the ability to download is included, so in most cases we will have to be content with MP3. Let's take a closer look at what we have.

Using the test sample, Adobe Audition, EncSpot and some other tweaks (which I described in detail in my article ), I was able to find out that SoundCloud currently uses LAME version 3.99.3 (strange, for 5 years as available 3.99.5 , and recently released 3.100 ) with preliminary resampling of the material to 44.1 kHz. In this case, resampling is performed by an algorithm that is clearly of higher quality than the one built into LAME. On the spectrogram of the sample I encoded (parameter --resample 44.1), aliasing is visible, but the sample with SC does not have it:

Well, at least for this, developers can say thanks.

The rest - the results, to put it mildly, not very. On the basis of noise (about -87 dBFS) in areas where silence was originally, we can conclude that processing and encoding were performed with an accuracy of 16 bits (this led to an increased quantization noise). For LAME, only the -b 128 parameter was used — the coding in the CBR is 128 kbps with an algorithm quality value of 3 (the highest quality is 0).

Conclusions may be as follows:

1. The developers did not use more efficient modes - VBR - since VBR V2 and V3 give a bitrate much higher than 128 kbit / s, and at lower bitrates the VBR model is not so effective and often even loses CBR. That is, in this case, the choice was made in favor of saving disk space, rather than encoding speed (VBR is encoded faster).
2. To save speed, the developers did not improve the quality of the algorithms (at least up to -q 2) and, apparently, for the same reason turned on an alternative reseller - the built-in LAME works rather slowly.

However, it may well be that no one at all thought about anything like that, and they only hammered in a parameter for encoding at 128 kbps, following the popular opinion about the transparency threshold on a given bitrate.

But what exactly is a reluctance to introduce new technologies. The currently leading Opus Codec encodes MP3 at least twice as fast, gives 128 kbit / s (or even 80-96) full transparency of the sound and is supported by all modern browsers (and its implementation on mobile platforms, thanks to openness, does not will work).

What we have now is low-quality MP3 audio that sounds audible distortions on any material or equipment of any quality. As a result, there is a paradox: the decision to lay out music on YouTube not designed for this will be better than putting it on a specially created SoundCloud.

But I still hope that the guys from SoundCloud will cope with the financial difficulties now underway, take up the mind and correct such annoying flaws.

PS And here the musicians themselves complain about the sound quality of SC: www.gearslutz.com/board/mastering-forum/664602-soundcloud-struggling-sound-quality.html