SoundCloud Sound Quality Research

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    In 2014, I conducted a detailed study of sound quality on YouTube (the material is still very relevant, there were no serious changes on YouTube during this time), shortly before that I checked how high-quality music is played on VKontakte social networks. In the same article, I examine the sound quality on a service designed exclusively for music - SoundCloud .


    But first, a brief historical excursion:

    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. The service was rapidly gaining popularity: in 2010, the number of users reached one million, and in 2013 exceeded 40 million (the number of listeners per month exceeded 170 million). However, SoundCloud continued to be the sole way for musicians to spread theirmusic, and it was impossible to download music protected by copyright. Negotiations with music companies have been unsuccessful for a long time. In 2014, it was possible to conclude an agreement with the Warner Music Group, but the labels were very skeptical about SoundCloud. Only in 2016, SoundCloud finally established cooperation with two other members of the Big Three - Universal Music Group and Sony Music Entertainment, which allowed to increase the amount of available content to more than 150 million tracks and launch the SoundCloud Go music service (currently available in the USA, Canada, France, Germany, the Netherlands, Great Britain, 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 and everything has led to the fact that people have simply become too lazy to download music from trackers, file hosting sites, etc. (everyone has already forgotten about buying disks) - after all it’s easier to drive the name of the track into the search for VK, YouTube, Yandex.Music, etc., press the Play button and not worry about anything else.


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


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    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 about to download / listen, but then I noticed a link on SoundCloud in the description - supposedly the mix was laid out there initially. I decided that it is better, as they say, to refer to the source, and clicked on the link.


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


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    Spectrograms vary widely - Opus has a wider spectrum, and this suggests that the downloaded 128-kb MP3 is not the primary source.


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


    I signed up for SoundCloud and uploaded a RightMark Audio Analyzer test signal in 24-bit / 96 kHz FLAC format:


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    By the way, PCM, FLAC, ALAC, OGG (Vorbis, Opus), MP3, AAC, and WMA are available for unloading from HQ formats (we do not take AMR and MP2 into account) - it is a little disappointing that there are no additional lossless formats (Monkey's Audio, WavPack).


    After downloading, I downloaded the track with the same button - also downloaded MP3 128 kbps. I checked and found out that this is exactly the material that is streamed when the playback starts. By the way, it’s better to still play it, after downloading and running it, for example, in foobar2000 (provided that it is configured correctly ) - this way you will protect yourself from additional quantization noise (the browser decodes in 16-bit PCM, foobar2000 - in 32-bit float ) and clipping (musicians are advised to normalize tracks to -3dBFS before uploading to SC, but not everyone does).


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


    Digging on the Internet, I found out that to be able to download the original of your 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:


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    This can be done for both private and public records.


    Well, that is already pleasing. But there are very few records on the service for which the download option is enabled, so in most cases we will have to be content with MP3. Let’s take a closer look at what we have.


    Using a test sample, Adobe Audition, EncSpot, and some other tricks (which I once described in detail in my article ), I was able to find out that SoundCloud currently uses LAME version 3.99.3 (strange, after 5 years 3.99.5 has been available for 5 years , and recently released 3.100 ) with preliminary resampling of the material up to 44.1 kHz. At the same time, resampling is performed by an algorithm that is clearly better than the built-in LAME. In the spectrogram of the sample I encoded (parameter --resample 44.1), aliasing is visible, but the sample with SC does not:


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    Well, at least you can say thanks to the developers.


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


    The findings may be as follows:


    1. Developers did not begin to use more effective modes - VBR - since VBR V2 and V3 give a bitrate significantly higher than 128 kbps, 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 to -q 2) and, apparently, turned on an alternative resamper for the same reason - the built-in LAME works quite slowly.


    However, it may well be that no one even thought about anything like that, and they just drove a parameter for encoding at 128 kbps, following the popular belief about the transparency threshold for this bitrate.


    But what exactly is the reluctance to introduce new technologies. The leading Opus Codec now encodes at least twice as fast as MP3, provides 128 kbps (or even 80-96) full transparency of sound and is already supported by all modern browsers (and its implementation on mobile platforms, thanks to its openness, does not amount to labor).


    The same that we have now - low-quality MP3 audio that sounds with audible distortion on any at least any high-quality material and equipment. As a result, a paradox emerges: the decision to upload music to YouTube that is not intended for this will be better than to upload it to a specially created SoundCloud.


    But I still hope that the SoundCloud guys will cope with the financial difficulties they are experiencing now, will tackle the mind and fix 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


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