5 ms·

Audio from Scratch with Go: Stereo Panning

116 points by Insanity 6y ago

sramsay 6y ago
Wow, this is really cool. I wonder how far the author plans to go with this? DSP gets pretty complex pretty quickly . . .
- Insanity 6y ago
  Her, author here! :) Glad you liked it! I don't have concrete plans actually, just doing this for fun so we'll see how far I get :)
  - nkozyra 6y ago
    Might have been an interesting point to stream this data (basic sine) to an audio output instead of file. That's more immediately hands on. (Sorry, this refers to the first entry in your audio/go series)
    - Insanity 6y ago
      Thanks, that's a good idea!
    - slx26 6y ago
      that can easily get pretty tricky if you don't want to depend a lot on libraries, which the last time I checked weren't great for golang in this area. I have worked with ALSA (advanced linux sound architecture) a bit, implementing basic midi input from a keyboard + sound generators + plugins with go interfaces and pkg/plugin + stream to audio output... and it's a mess of devices, buffers and formats. and that's only for one OS. and if you start doing anything non-trivial, making the programs work well in real-time is not for the faint of heart. if there was a single format supported everywhere, minimum buffer sizes and a common API for all OSes, it would be a whole another, much more pleasant story
PaulDavisThe1st 6y ago
[ Edited/Deleted reply because I missed the fact that this code distributes a single mono signal across 2 outputs. The terminology for this stuff is never totally clear: some people would call this a mono panner, some would call it a stereo panner, some call it a 1in/2out panner ]
- Insanity 6y ago
  Hey there, yep I'm actually aware of what you're saying. I actually wrote this at the bottom of the post: "There is actually a flaw with this panning function that we are using. However it is not apparent to us yet because we can only set a pan for an entire audio source" I'm working from something simple up to something more complex, but tackling it in small parts. Next I'm writing about applying breakpoints where the pan can be set throughout the track and you can notice the power dip - and then we'll work on fixing that. ;-)
  - deleted 6y ago
    [deleted]
  - PaulDavisThe1st 6y ago
    For some reason, I just realized that despite your talk about 2 channel WAV files, this code is actually a 1 input to 2 output panner. So I take back what I said about it being a balance control entirely. Sorry for that.
- deleted 6y ago
  [deleted]
akx 6y ago
Wonder if this should take into account pan laws: * https://en.wikipedia.org/wiki/Pan_law https://en.wikipedia.org/wiki/Pan_law * https://www.image-line.com/support/flstudio_online_manual/html/songsettings_settings.htm https://www.image-line.com/support/flstudio_online_manual/ht... (search for "panning law")
- pierrec 6y ago
  I believe this minimal implementation actually over-compensates for pan law because it has a -6dB center. In other words, if you ask this tool for zero panning, it will actually divide the amplitude by 2 (probably not what most people would expect!) In DAWs, -3dB or 0dB center is more common. In a tool like this I would suggest a 0dB center by default, so that zero panning does not change the amplitude. This would be what you second link calls triangular pan law.
mgraczyk 6y ago
This is a fun tutorial for processing audio in Go, but generally panning will sound bad if you only adjust the amplitude/level. The two important missing pieces are phase delay and frequency-specific attenuation (the "head" model). Audio coming from the left side of your head reaches your left ear first, then your right ear later. Also, your head blocks certain frequencies more than others. Both of these effects are super noticeable and necessary to make panning sound "3D". Adding these things to the Go code would actually be fairly straightforward, you just need to add a filter to `applyPan`. The filter would only need around 12 taps to sound good. Here's a javascript tutorial which includes both of these additional features: https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Web_audio_spatialization_basics https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_A...
- qmmmur 6y ago
  You say this like it's bog standard but adding HRTF and compensation for speaker distance are not part of a standard panning algorithm. This is more likely to exist in another module, such as for ambisonics or correction.
  - TheOtherHobbes 6y ago
    HRTF is often used in game audio and AR [2], but never [1] as a mix effect in commercial DAWs. HRTF is a blunt instrument anyway. It's supposed to model your head and not just a standard imaginary generic head, and that's impossible without sticking a microphone inside each ear. It's also a headphone-only effect. As soon as you play the sound through speakers you get room reflections and all kinds of other artefacts which wash out the spatial detail. [1] Almost never. There are HRTF plugins, but they're hardly ever used in music mixing. [2] Apple has some HRTF patents for recording audio on multiple channels - not just two - using HRTFs to capture apparent depth.
    - qmmmur 6y ago
      Sorry this is just wrong. What is your basis for saying that HRTF are never used in commerical DAWs? Have you read anything by Bob Katz or Rashad Becker? Or perhaps you're not aware of the several options people reach for to perform multichannel mixing using ambisonics: https://plugins.iem.at/ https://plugins.iem.at/ https://www.ssa-plugins.com/ https://www.ssa-plugins.com/ http://www.ambisonictoolkit.net/documentation/reaper/ http://www.ambisonictoolkit.net/documentation/reaper/
BookPage 6y ago
Having had to do some mass audio stuff on datasets recently I discovered SoX - a self proclaimed "swiss army knife" for sound processing. Delighted to find multiple bindings in Go, I eventually decided to just do it in python as there was a very solid library there and it was just simpler for my use case.
- tekstar 6y ago
  The command line application is also quite useful. Usually you wouldn't need to go into a programming language at all to wield its power
  - BookPage 6y ago
    Yeah you're right it is. I was strongly considering just writing a bash script but I had a bunch of probabilistic stuff going on for using effects, so stuck with python.
    - tekstar 6y ago
      I've had good luck writing ruby scripts that just shell out to Sox because I didn't feel like learning the API

116 points by Insanity 6y ago

Wow, this is really cool. I wonder how far the author plans to go with this? DSP gets pretty complex pretty quickly . . .

Insanity 6y ago
Her, author here! :) Glad you liked it! I don't have concrete plans actually, just doing this for fun so we'll see how far I get :)
- nkozyra 6y ago
  Might have been an interesting point to stream this data (basic sine) to an audio output instead of file. That's more immediately hands on. (Sorry, this refers to the first entry in your audio/go series)
  - Insanity 6y ago
    Thanks, that's a good idea!
  - slx26 6y ago
    that can easily get pretty tricky if you don't want to depend a lot on libraries, which the last time I checked weren't great for golang in this area. I have worked with ALSA (advanced linux sound architecture) a bit, implementing basic midi input from a keyboard + sound generators + plugins with go interfaces and pkg/plugin + stream to audio output... and it's a mess of devices, buffers and formats. and that's only for one OS. and if you start doing anything non-trivial, making the programs work well in real-time is not for the faint of heart. if there was a single format supported everywhere, minimum buffer sizes and a common API for all OSes, it would be a whole another, much more pleasant story

PaulDavisThe1st 6y ago

[ Edited/Deleted reply because I missed the fact that this code distributes a single mono signal across 2 outputs. The terminology for this stuff is never totally clear: some people would call this a mono panner, some would call it a stereo panner, some call it a 1in/2out panner ]

Insanity 6y ago
Hey there, yep I'm actually aware of what you're saying. I actually wrote this at the bottom of the post: "There is actually a flaw with this panning function that we are using. However it is not apparent to us yet because we can only set a pan for an entire audio source" I'm working from something simple up to something more complex, but tackling it in small parts. Next I'm writing about applying breakpoints where the pan can be set throughout the track and you can notice the power dip - and then we'll work on fixing that. ;-)
- deleted 6y ago
  [deleted]
- PaulDavisThe1st 6y ago
  For some reason, I just realized that despite your talk about 2 channel WAV files, this code is actually a 1 input to 2 output panner. So I take back what I said about it being a balance control entirely. Sorry for that.
deleted 6y ago
[deleted]

akx 6y ago

Wonder if this should take into account pan laws: * https://en.wikipedia.org/wiki/Pan_law https://en.wikipedia.org/wiki/Pan_law * https://www.image-line.com/support/flstudio_online_manual/html/songsettings_settings.htm https://www.image-line.com/support/flstudio_online_manual/ht... (search for "panning law")

pierrec 6y ago
I believe this minimal implementation actually over-compensates for pan law because it has a -6dB center. In other words, if you ask this tool for zero panning, it will actually divide the amplitude by 2 (probably not what most people would expect!) In DAWs, -3dB or 0dB center is more common. In a tool like this I would suggest a 0dB center by default, so that zero panning does not change the amplitude. This would be what you second link calls triangular pan law.

mgraczyk 6y ago

This is a fun tutorial for processing audio in Go, but generally panning will sound bad if you only adjust the amplitude/level. The two important missing pieces are phase delay and frequency-specific attenuation (the "head" model). Audio coming from the left side of your head reaches your left ear first, then your right ear later. Also, your head blocks certain frequencies more than others. Both of these effects are super noticeable and necessary to make panning sound "3D". Adding these things to the Go code would actually be fairly straightforward, you just need to add a filter to `applyPan`. The filter would only need around 12 taps to sound good. Here's a javascript tutorial which includes both of these additional features: https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Web_audio_spatialization_basics https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_A...

qmmmur 6y ago
You say this like it's bog standard but adding HRTF and compensation for speaker distance are not part of a standard panning algorithm. This is more likely to exist in another module, such as for ambisonics or correction.
- TheOtherHobbes 6y ago
  HRTF is often used in game audio and AR [2], but never [1] as a mix effect in commercial DAWs. HRTF is a blunt instrument anyway. It's supposed to model your head and not just a standard imaginary generic head, and that's impossible without sticking a microphone inside each ear. It's also a headphone-only effect. As soon as you play the sound through speakers you get room reflections and all kinds of other artefacts which wash out the spatial detail. [1] Almost never. There are HRTF plugins, but they're hardly ever used in music mixing. [2] Apple has some HRTF patents for recording audio on multiple channels - not just two - using HRTFs to capture apparent depth.
  - qmmmur 6y ago
    Sorry this is just wrong. What is your basis for saying that HRTF are never used in commerical DAWs? Have you read anything by Bob Katz or Rashad Becker? Or perhaps you're not aware of the several options people reach for to perform multichannel mixing using ambisonics: https://plugins.iem.at/ https://plugins.iem.at/ https://www.ssa-plugins.com/ https://www.ssa-plugins.com/ http://www.ambisonictoolkit.net/documentation/reaper/ http://www.ambisonictoolkit.net/documentation/reaper/

BookPage 6y ago

Having had to do some mass audio stuff on datasets recently I discovered SoX - a self proclaimed "swiss army knife" for sound processing. Delighted to find multiple bindings in Go, I eventually decided to just do it in python as there was a very solid library there and it was just simpler for my use case.

tekstar 6y ago
The command line application is also quite useful. Usually you wouldn't need to go into a programming language at all to wield its power
- BookPage 6y ago
  Yeah you're right it is. I was strongly considering just writing a bash script but I had a bunch of probabilistic stuff going on for using effects, so stuck with python.
  - tekstar 6y ago
    I've had good luck writing ruby scripts that just shell out to Sox because I didn't feel like learning the API