Embed scope audio visualization 🝚

Intro / Angles of incidence

As events go in the lifes of over-associating headcases, down in the crypt doing some Gullibloon archeology. While making sure not to double release on a track, digging out the pxp track published on a compilation CD by the Alienation label in 2002 [1].

While listening to the track starting to play with audio scopes, looking for a real time vectorscope (aka phase scope). ‘meterbridge’ is OK but not totally satisfying, so moving on to jack-scope [2]. We are on Linux and are using the Jack Audio Connection Kit [4]. Seconds before ditching jack-scope, attention tangles up in the -m option for setting the scope operating mode. Clipping the manual entry for drama,

-m : Set the scope operating mode (default=signal). The operating
modes are: signal and embed.

⚠ Ugh! Being in a relationship with ‘embed’ its name screams dopamine-ahead at me 🚨.

Embeddings

Embedding is a mathematical name for a family of structure-preserving maps. Don’t run yet, because everyone knows embeddings as a thing of experience and this is only another name for it. As an example of an embedding present in a real life process, take

A set of counters each serving one customer taken from a queue of incoming customers arriving at a shop.

If you know what a delay line is, that’s your embedding too. Same for moving average and sliding window operators. What a delay line does, besides delaying the stuff going into it, is create a map from single consecutive events at several moments in time to a set of several simultaneous events in a single moment of time. In the standard use case this is not apparent because the delay line is only tapped at the end, but the term ‘line’ tells it. The sum delay at the end is created using a line of unit delays. Thinking multitap delay the embedding comes out clearly. 🝚

TODO: picture

For sound visualization of a single channel signal which provides a single number at every instant, we can use a delay line with two elements and draw a dot at the two-dimensional coordinate made from the current and the last number. Thats the basic principle, everything else is parameters.

TODO: picture

Embed mode with jack-scope

Now jack-scope can do embed mode visualization from a jack audio signal. Did that for the pxp - squeezer-2002 and recorded a screen cap of that which you can watch below or on https://youtu.be/BQRzuW0mlBo.

It works very well to indicate general phase coherence for example. The more of that, the more stable the point cloud becomes. Apart from that it makes awesome patterns on these drone things with ultra low modulation depth. While the points’ visibility and rendering could be improved I suggest to contemplate the frailty as a charm in this episode.

The command used for creating the scope in the video is

jack-scope -m embed -n 2 -d 20 -p PortAudio:out_\%d

where the track is playing from audacity on the PortAudio jack terminals. The man-page has a link to a paper on the technique [3] which is paywalled. If you join our audio research group the document can be shared. Also discovered only while writing this up that bwo my OS version I am using a slighly old or underdocumented version of jack-scope compared with [2]. A nice feature of jack-scope is that many visualization parameters can be controlled at run time via OpenSoundControl commands. Ha! Awesome.

Relevance

I have known and used embedding technqiues for years but it never occured to me to use it on the single sample level and look for, or make, tools to do that. Maybe in commercial music software land it’s a commodity that everyone’s using up and down. I think the embed scope technique is little known and used and this is the reason for writing this. Check if your scope has that and if not, talk to your scope vendor and drop them a feature request. Please leave a comment on this page about any findings or reports you might be able to share, curious to learn.

Future work

Building autovideo I have become a daily user and passionate lover of ffmpeg. Obviously, an aembedscope is needed. Have never done an ffmpeg plugin but should be possible. Keep you posted and please let me know if you happen to be working on that or even have it ready to use.

See also and further reading

[1] Alienation Presents: International Compilation CDr4, SU40 https://www.discogs.com/Various-Alienation-Presents-International-Compilation-CDr_4/release/1356487, see also SU06 on https://www.discogs.com/Various-Alienation-Presents-International-Compilation-CDr/release/116676

[2] rju - jackd utilities, http://rohandrape.net/?t=rju

[3] Sound Visualization Using Embedding: The Art and Science of Auditory Autocorrelation, Monro and Pressing, 1998, CMJ, https://www.jstor.org/stable/3680961

[4] Jack Audio Connection Kit, https://jackaudio.org/

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