
What Does Perlin Noise Sound Like? - 10098
http://gpfault.net/posts/perlin-sound.txt.html
======
rubatuga
Running it through a FFT, the noise looks similar to blue noise, but with a
lowpass at 1000 Hz

------
failrate
Unfortunately, the audio clips do not play in Safari mobile.

~~~
danblick
Why does Safari struggle to open files in common and free formats?

~~~
derefr
AFAIK iOS (and tvOS) devices only support playing formats+codecs with native
hardware decoder support; they don't have any pure-CPU decoding
implementations.

This, from what I recall, was an intentional choice to disincentivize
developers from making the "easy choice" to ship assets in the same
format+codec for all devices, where such a format would burn the iOS device's
battery doing CPU decoding. Instead, most developers will choose to separately
encode their assets for iOS, so that they can use the iOS media
frameworks—which coincidentally means that they'll be using the efficient
hardware encoding and not burning much battery at all.

However, you _can_ ship custom CPU decoding in your app if you want (e.g.
VLC.ipa).

Websites, obviously, aren't ( _usually_ ) built for single architectures,
though, so it's a bit of a pain for them. Larger web video providers (most
porn sites, for example) keep iOS-specific encodings on their CDN and try to
detect the browser's user agent to decide which version to deliver. Other
providers just give up on the concept and build specific iOS-specific apps in
order to ensure the correct media is delivered (this being why there are more
"video-sharing site" apps for iOS than for Android.)

~~~
tinus_hn
When iOS was first released everybody and his dog was still running their own
proprietary movie (container) format. Microsoft was pushing .wmv, websites
used Flash, illegal sources were using .avi files.

Apple forced these sites to provide their streams in a standardized format,
MP4.

It might not be the standard you want because it isn't patent free but at
least it is a standard, it's not controlled by Apple and it works on just
about any device and works pretty well.

------
tscs37
This sound kind of reminds me of one of these "Space Engine Sounds" on
youtube, especially the Firefly/Serenity themed track.

I used to love it for sleeping, it's rather relaxing.

~~~
lloeki
To me the first sample sounded like some subway passing by but when you're
still far away yet.

That said, after about 15 to 30s of attentive, continuous listening, it
started making me increasingly uneasy, as I perceived the sound as being
extremely oppressive and ominous, in a very chthonian way. I'm not going to
try to listen to that any longer because I'm half sure that could almost turn
into a panic attack of sorts or something. Really unsettling.

The second, fractal one didn't produce that effect unless I turned the volume
_way_ up, and even then, not as much.

~~~
aisofteng
The concept of getting a panic attack in response to listening to some audio
is completely foreign to me. Is it normal to have that reaction? It sure seems
like it wouldn't be.

~~~
nice_byte
IIRC there's some evidence that very low-frequency sounds may cause feelings
of anxiety and fear in human subjects. Very low frequency sounds may occur
prior to catastrophic events like earthquakes, and some animals have been
known to react to it. It's plausible that humans have evolved a similar
protection mechanism which has gradually atrophied. That being said, I'm
talking about sub-20 Hz frequencies here. I don't think these recordings
contain that and I don't think it would be possible to reproduce on regular
headphones anyway...

~~~
lloeki
Missing funtamentals are a thing though.

[0]:
[https://en.wikipedia.org/wiki/Missing_fundamental](https://en.wikipedia.org/wiki/Missing_fundamental)

------
Kenji
My initial reaction was like "Oh, like white noise!"

I could not have been more wrong. There is very clear structure in Perlin
Noise. Great write-up and I learned something.

~~~
jjoonathan
The article doesn't adjust for the inherent lowpass/highpass/aliasing behavior
of function parameter rate vs sample rate, which is responsible for most of
the audible difference, especially the similarities to real life low-passed-
noise situations (airplane cabin, high building) noted by the author. Still, I
agree, you can hear some residual tones!

Spectra of the 3 noise samples:
[http://imgur.com/a/gaiVm](http://imgur.com/a/gaiVm)

I haven't read up on perlin noise recently enough to know whether that's
inherent to its structure or whether there's a more mundane explanation like
distortion or encoding tomfoolery.

~~~
nice_byte
Thanks for the spectrograms! I'm not exactly sure which aliasing you're
referring to... I'm trying to adjust the sampling rate of the noise function
so that it maps to "real" seconds in a way that makes sense. By looking at the
waveform in the audio editor, it looks exactly like a visual representation of
1D perlin noise to me ([http://imgur.com/a/bM4tn](http://imgur.com/a/bM4tn)).
Looking at your spectrograms though, I'm seeing something in the higher-
frequencies (and I think I can hear those as well), but I actually have no
explanation for where those could have come from.

~~~
jjoonathan
That's a completely reasonable thing to do, especially because it might allow
you to pick up distortion due to interpolation.

However, you should do the same thing to the white noise [1] if you are going
to compare them. If we write the white noise's continuous reconstruction [2]
as a function of time, w(t), we could stretch out w(t) until it wiggles at
about the same rate as the perlin noise, p(t), and then sample them together
at a rate several times higher than that at which they wiggle. Both waveforms
would then have the same "muffled roar" sound you get in airplanes, buildings,
underwater, etc.

Another mundane explanation for the bands is that they might be "JPEG
artifacts" for ogg's compression. Amplitude is logarithmic, so they're
probably not as important as they look.

[1] To be pedantic we should call it band-limited white noise, because the
sampling+reconstruction process limits the bandwidth, and infinite bandwidth
white noise can't actually exist, because it has finite energy per bandwidth *
infinite bandwidth = infinite energy. This isn't a theoretical problem.
Oscilloscopes have fatter "no-signal" traces in proportion to their bandwidth,
the resolution bandwidth ("RBW") of spectrum analyzers lifts the noise floor
at higher settings, the field of thermodynamics fell apart in the "ultraviolet
catastrophe" before we understood how quantum mechanics effectively limits the
bandwidth of thermal radiation, etc.

[2] w(float t) rather than w(int n), obtained by interpolation. Sinx/x
interpolation is the interpolation that gives 0 distortion and produces no
higher spectral content. It's the time domain equivalent of doing a Fourier
Transform, scaling the spectrum, and doing an Inverse Fourier Transform. IIRC
Perlin noise is a spline, not sinx/x, so I'd expect its interpolation to
produce higher harmonics. By applying perlin-like (spline?) interpolation and
sinx/x interpolation to the white noise, you could isolate the audio effects
due to the randomization vs the interpolation of the perlin noise. If you were
so inclined :)

------
andai
I've heard this before! In some Nine Inch Nails tracks. I always thought it
was white noise + bandpass + clipping or distortion.

~~~
shawnz
> I always thought it was white noise + bandpass

That would be equivalent to this approach, right?

------
hammock
Didn't really understand how he got to it, but would be interesting to hear
this noise source across the larger spectrum (not just the low freqs)

It might sound/be more natural/fractal than pure white noise (+LPF), I can't
tell. But it won't work to drown out office chatter because its the high freqs
there that matter.

------
slaymaker1907
It might be interesting to use Perlin noise to craft a melody by mapping the
reals onto a musical scale.

In particular, it seems like it would have some nice properties for melodies
since it will keep the melody in a comfortable range and won't throw in a
bunch of large leaps.

------
blue1
To me it sounds like the ships background noise in Star Trek.

------
joshu
Does this use Perlin noise to generate the PCM values?

If so, what would it look like to use Perlin noise as the input to an inverse
FFT function?

------
martyvis
LOL. I just finished putting up a pergola with a clear polycarbonate roof. The
recommendation is to apply a foam adhesive tape to the purlins (battens) to
prevent noise caused by movement of the sheets from thermal expansion.
I[https://www.bunnings.com.au/suntuf-
access-25mm-x-20m-purlin-...](https://www.bunnings.com.au/suntuf-
access-25mm-x-20m-purlin-tape_p1010469) \- I thought it was a strange topic
for HN ;-)

