
Encoding data into dubstep drops - benjojo12
https://blog.benjojo.co.uk/post/encoding-data-into-dubstep-drops
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cyanoacry
Neat, it's always really cool to see folks get their feet wet in the DSP
field! (Props to the author for trying to get through the dense Wikipedia
pages.)

Minor correction for the author: this isn't amplitude-shift keying, and the
way to tell is to look at how demodulation works. The detection code asks if a
sample is negative or positive, but "how large is this sample?" is never
asked. An ASK demodulator effectively thresholds the signal on amplitude and
in the simplest case this boils down to "is there a signal or not?"

The implemented code has some flavor of phase-shift keying (the inversion of a
sine wave flips the phase 180 degrees), but since there isn't guaranteed to be
a steady carrier, it seems like it'd be hard to decode as a pure PSK. The all-
sample offset (constant above or below zero) can also be treated in a way as a
PSK process, with the carrier being DC (0Hz).

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psonic
Check Aphex Twin - Equation if you haven't already
[https://www.youtube.com/watch?v=M9xMuPWAZW8](https://www.youtube.com/watch?v=M9xMuPWAZW8)

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hansjorg
For the impatient, skip towards the end (zinger at 5:20):

[https://youtu.be/M9xMuPWAZW8?t=295](https://youtu.be/M9xMuPWAZW8?t=295)

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jdpigeon
Since the data is being encoded with a signal processing trick that is
inaudible to human ears this could work in any song with 0-100hz frequencies,
right?

I was little disappointed when I didn't hear intense dialup-modem-like sounds
encoding data I'm the midrange

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MertsA
It's not inaudible. Human hearing extends down to around 20Hz but also some
speakers have terrible frequency response down that low so it might mask it
better but the tone isn't low enough to be completely inaudible.

~~~
mistersquid
Comparing the before and after samples, there is definitely an audible
difference for this pair of ears.

To be fair, I listened to the after sample first and it sounded like regular
old Skrillex to me.

I scrolled up and listened to the before sample and noticed that the bass was
deeper and more harmonious with the higher end frequencies. Basically, the
original sample has a "subsonic" vibrations that resonate in time and
"harmony" with the higher end sounds. (Also, I'm using higher-end earphones
with custom ear canal sleeves to listen.)

So, I probably wouldn't have noticed anything unusual if I'd only listened to
the modified bass drop, but I can hear the difference when comparing the two.

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jbeckham
I'm pretty sure that this would drop the volume of the 0-100hz range to half
the volume since we dropped the amplitude to 1/2 and shifted. Any sound system
with loud subwoofers would be able to detect the difference, but woofer only
systems would probably leave the modification mostly undetectable.

~~~
phobius
spot on. also there's likely to be some phase issues in some mixes

aside: seems to be a smooth enough lerp between bits so as not to destroy
speakers, but might cause a record needle to jump (can anyone more versed
weigh in here?)

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plussed_reader
Great article about encoding; this is similar to the DRM the PS3 uses on video
content. It's a low bit rate signal, but after enough time of the movie
playing enough bits are generated to trigger the DRM flag and stop playback.

~~~
gsich
Cinavia is similar:
[https://en.wikipedia.org/wiki/Cinavia](https://en.wikipedia.org/wiki/Cinavia)

Can't find stuff about Digital Restriction Management for the PS3, you sure
there was something inside the video stream?

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asherkin
Pretty sure they're talking about Cinavia, as the PS3 was one of the most
well-known implementors of it.

~~~
gsich
Yes, but that's in the audio signal.

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aristocles
Very cool. I suspect there is something unique going on with dubstep "drops"
and dopamine release. There is a reason it engages peoples basest systems.

~~~
overcast
"drops" have their equivalent in every other form of music. Breakdowns in
hardcore, choruses in pop music, it's just a catchy part of any tune that
people easily grab onto.

~~~
anamexis
Drops certainly have equivalents in other music, but I don't think those are
good comparisons.

I don't think the defining feature of drops is their catchiness, but the
slowly building tension and sudden release.

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cat199
> Drops certainly have equivalents in other music, but I don't think those are
> good comparisons.

seriously?

dubstep is just 'another' form of eletctronic dance music..

and, to be opinionated, basically rhythmically dumbed-down drum&bass which
itself is rhythmically dumbed down jungle which itself is rhythmically more
complicated hardcore techno minus the 4-to-the-floor bass drums of the 'main'
tune...

also: get off my lawn. :b

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anamexis
I wasn't making any value judgments about dubstep or anything else, I was
discussing the definition and semantics of what a 'drop' is.

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pattrn
It felt very strange reading this, as it was nearly identical to a project I
did in college for a class about discrete time signal analysis. We had to
decipher encoded messages embedded within Crawling in the Dark by Hoobastank.
The sound clip was: "is there something more than what I've been handed?"
Funny professor.

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andrewmcwatters
We miss you over at Facepunch, Ben. Good to see WAYWO on HN, though. Hope
you're doing well! :)

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phobius
does the hive mind know what the commandline tool is that he used for
displaying audio spectrum?

(or @benjojo12 if you're watching... your setup has inspired me, and I want to
play)

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cmonfeat
While reading the post I kept thinking "this would be a really cool project to
present at RC." Then I saw the end :)

Cool project!

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heywire
This is super cool! I really enjoyed the animations in your writeup as well.
Thanks for sharing!

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mirap
How about mp3 (or other) compression? Would not the information be lost?

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gelo
the codecs in most lossy compression formats usually nuke the phase
information so here in this example as ASK is being used there isnt any lost
of information. If he tried to encode phase changes in the sound then you
wouldnt recover it since the decoder regenerates the audio with 0 deg phase.

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mistercow
What do you mean by "nuke the phase information"?

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vardump
Probably just that mp3 compression loses phase information? As it indeed does.

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mistercow
Can you elaborate? What specifically about mp3 compression causes the phase
information to be lost? Clearly, if you simply take IDCT(DCT(s)) for some
signal s, you don't lose phase information, because the DCT is invertible. So
are you saying that quantization causes the phase information to be lost? If
so, why do binaural recordings still work fine when compressed as mp3s, given
that they depend heavily on phase differences between the sounds reaching each
ear?

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vardump
> If so, why do binaural recordings still work fine when compressed as mp3s,
> given that they depend heavily on phase differences between the sounds
> reaching each ear?

That's a very good point. If phase information is lost, low frequency stereo
sound localization should indeed suffer.

Also discrete cosine transformation indeed keeps phase.

I guess mp3 shouldn't be losing phase information after all.

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ixtli
worth noting that causing a speaker to vibrate around .5 and -.5 for a bit and
then quickly swapping might mess with high end hardware. super cool though.

~~~
jstanley
Surely it's more likely to mess with low-end speakers?

Wouldn't high-end speakers be built to withstand anything within their
operating range?

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Avery3R
They're built to create sound, not hold themselves in one direction for an
extended period of time

