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Surround

Surround Sound in Music


I have been doing some exploration in to quadraphonic audio.

Quadraphonic is a system that never got formalized as a standard. The closest standard that you find is 5.1 or 7.1 sounds system that you find in home theater systems. You can fit a quadraphonic sound, 4 channels, into a 5.1 system, however the left and right speakers for front and back, in a 5.1 systems often are not placed in a perfect square.
The back speakers are called surround speakers, because they are just slightly at the back of the listener. They are also for added ambiance in movies, they are not necessarily a full sound source.
Still Stereo, 5.1 and 7.1 are source based system. You render the sound for the location of your speakers.
This is changing with Dolby Atmos which is an object based sound system: what are the objects in your virtual 3D that emit sounds, they then get rendered on any speaker configuration.

Let's get back to quadraphonics.
I rendered a quadraphonic track into various formats and uploaded to YouTube:


I use a utility called youtube-dl to see what YouTube did of the files.

  • the audio of the 360 video is rendered, mainly on headphones, based on what the listener is watching. It is not great for TVs, YouTube in fact does not render the 360 view on TV players.
  • the 4 channels is downmixed to 2 stereo channels
  • the stereo or binaural stay in their format
  • the 5.1 channels exist in downmixed stereo and in 5.1. Therefore the player could play either of the audio files.


If you look at the files created by YouTube for the 5.1 upload you see that the larger sizes are in 5.1.

$ youtube-dl --list-formats https://www.youtube.com/watch?v=rPODqX7JW5M
[info] Available formats for rPODqX7JW5M:
format code  extension  resolution note
249          webm       audio only DASH audio   66k , opus @ 50k, 2.16MiB
250          webm       audio only DASH audio   88k , opus @ 70k, 2.85MiB
140          m4a        audio only DASH audio  130k , m4a_dash container, mp4a.40.2@128k, 4.59MiB
251          webm       audio only DASH audio  173k , opus @160k, 5.61MiB
256          m4a        audio only DASH audio  196k , m4a_dash container, mp4a.40.5, 6.92MiB
258          m4a        audio only DASH audio  389k , m4a_dash container, mp4a.40.2, 13.75MiB
160          mp4        256x144    144p   95k , avc1.4d400c, 30fps, video only, 2.03MiB
278          webm       256x144    144p  103k , webm container, vp9, 30fps, video only, 2.83MiB
242          webm       426x240    240p  237k , vp9, 30fps, video only, 4.28MiB
133          mp4        426x240    240p  292k , avc1.4d4015, 30fps, video only, 5.40MiB
243          webm       640x360    360p  448k , vp9, 30fps, video only, 9.15MiB
134          mp4        640x360    360p  663k , avc1.4d401e, 30fps, video only, 11.69MiB
244          webm       854x480    480p  883k , vp9, 30fps, video only, 15.74MiB
135          mp4        854x480    480p 1285k , avc1.4d401f, 30fps, video only, 23.93MiB
247          webm       1280x720   720p 1882k , vp9, 30fps, video only, 28.91MiB
136          mp4        1280x720   720p 2520k , avc1.4d401f, 30fps, video only, 50.56MiB
248          webm       1920x1080  1080p 2744k , vp9, 30fps, video only, 46.64MiB
137          mp4        1920x1080  1080p 4908k , avc1.640028, 30fps, video only, 77.85MiB
271          webm       2560x1440  1440p 7900k , vp9, 30fps, video only, 160.67MiB
313          webm       3840x2160  2160p 14994k , vp9, 30fps, video only, 259.44MiB
18           mp4        640x360    medium  507k , avc1.42001E, mp4a.40.2@ 96k (44100Hz), 18.00MiB (best)


I select to download format code 258, which is the biggest audio file in mp4 format and I check using ffmpeg its audio format and especially how many channels it has.

$ youtube-dl -f 258 "https://www.youtube.com/watch?v=rPODqX7JW5M"
[download] Destination: _-rPODqX7JW5M.m4a
[download] 100% of 13.75MiB in 00:03

$ ffprobe _-rPODqX7JW5M.m4a 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '_-rPODqX7JW5M.m4a':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6mp41
    creation_time   : 2019-10-14T08:21:16.000000Z
  Duration: 00:04:57.45, start: 0.000000, bitrate: 387 kb/s
    Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 12 kb/s (default)
    Metadata:
      creation_time   : 2019-10-14T08:21:16.000000Z
      handler_name    : ISO Media file produced by Google Inc.

As you can see the Stream #0:0 is 48kHz with 5.1 channels.

To help you test your sound system, I uploaded an original 5.1 movie on my site and using the HTML5 video tag, your browser should play the movie with all its channels.

This video uses HTML5 <video> element and is in mp4 format which is supported by all modern browsers.

<video width="100%" preload="" controls=""> 
          <source src="files/Surround-5.1.mp4" type="video/mp4; codecs="avc1.4D401F,mp4a.40.5"> 
          <span class="error">Error: Source Statement Failure - Format not supported in this browser?</span> 
</video>


I also uploaded this movie on YouTube:

However I tried to play it on my web browser, the youtube app on xfinity, or the youtube app on PS3 and all I got was the downmix stereo, despite the fact that a 5.1 format does exist on YouTube and that browsers are capable of rendering a movie with 5.1 audio.

Searching the Internet it appears that the PS4 may have a 5.1 YouTube player. Many people are commenting that YouTube TV does not play 5.1 movies like Netflix does, therefore they don't see the benefit of YouTube Movie premium.
So, will we see support for 5.1 on YouTube soon? time will tell.

You may have seen 5.1 videos on YouTube, and got the feeling that your sound system renders them in 5.1. Not exactly, these videos have only 2 channels, but there are a few ways to encode 4 or more channels into 2 channels using matrix encoding with optional phase shift(Wikipedia).

This is what Dolby Pro Logic II, also know as DPL II, does using matrix technology. On Amplifiers that do not understand DPL II the sound is just stereo with a relatively good quality downmix. You should be able to upload a DPL II video to YouTube and have the proper amplifier decode it into 5.1. DPLII seems widely supported as it seems it comes part of any movie sound system that has the Dolby logo. However, if you upload a 5.1 video, YouTube will not encode the audio in this format but just downmix it to stereo.

Waveforms of the 5.1 test file (L, R, C, LFE, LS, RS):
Surround5.1 Waveform

Converted to DPLII:
Surrounddplii Waveform

DPL II format is not without its challenges, after all there is lot of signal compression and mixing going on to fit 5.1 channels into 2 channels.

For other distributions systems, like Bandcamp, they only support stereo audio. What people have done, is offer a physical medium SACD or DVD to purchase or download a specific file from something like dropbox to get the quadraphonic or 5.1 file.

It seems that Sony is working with Deezer, Tidal and a few others to offer HiFi 360 Sound on selected Sony headphones. Will that take?

Additionally, companies are offering surround headphones, with many drivers per head. It seems the gaming industry has a marktet for players that want to hear what's happening in their back...

However if you want to listen to a quadraphonic or surround track in its perfect form, you still have to rely on physical media.