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Re: How hard can it be? Audio processing

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On 25/03/2021 01:01, Michael Haufe (TNO) wrote:
> On Tuesday, March 23, 2021 at 7:10:29 AM UTC-5, The Natural Philosopher wrote:
>> In principle audio processing in more or less real time is simple. You
>> need a 'call back' function that gets presented with one or more samples
>> of digital audio, and you return one or more samples of modified data,
>> modified by the state of some [global] variables (controls) and the
>> state of the sample, and previous ones...in essence that is ALL digital
>> signal processing does, or needs to do. The cleverness is in the
>> algorithms that do the modification.
>>
>> <rant>Until object orientation and computer scientists (after
>> ArtStudents™, the next most dangerous class to be allowed near a
>> computer) get in the way, and you need a 100k library just to even
>> change the volume.
>>
>> And as is usual with any API, the documentation tells you how to use it,
>> but never why you might want to, and invents a huge number of new
>> concepts that are completely unnecessary in order to preserve the
>> sanctity of the CodeGurus™ who wrote the damn thing.
>> </rant>
>>
>> So my question is this: what is the simplest and most minimal way to
>> 'intercept' a stereo audio stream - might be from a file, might be from
>> a radio station or live TV stream - in a browser and do so minimalist
>> signal processing that is NOT provided by some 3rd party library, but
>> actual self written code in terms of 'modify this sample dependent on
>> the state of a global variable or variables, and previous samples'
>>
>> Answers in less than 10k lines of code will get a virtual beer token
> 
> 
> With the current browser standards it looks like you can accomplish this in about ~100 lines of code or less:
> 
> <https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/frequencyBinCount#example>
> 
> The following code is a little out of date but still demonstrates a method of using a url as a stream:
> 
> <https://codepen.io/DonKarlssonSan/pen/bdNBMz?editors=0010>
> 
> The following is also slightly outdated but shows a method for processing microphone input:
> 
> <https://stackoverflow.com/questions/15940934/html5-capture-audio-from-default-microphone>
> 
> I think the following is the most fruitful. Still less than 100 lines:
> 
> <https://medium.com/swlh/building-a-audio-visualizer-with-javascript-324b8d420e7>
> 
> The outdated examples above need to be modified to request microphone input after a user initiated event:
> 
> <https://developers.google.com/web/updates/2017/09/autoplay-policy-changes#webaudio>
> 
First of all thank you for that, very much. It answers one half of the 
question which is 'can I work on stream as opposed to a file' and the 
answer would seem to be 'yes'

#But it doesn't actually answer the other half of my question - in
both cases I looked at there is a call to the unexplained, and 
undocumented function: e.g.

analyser.getByteFrequencyData(data);

Ok I discovered that as usual this is a 'API' function. That doesn't do 
what I want.

What I want to know is how to create a *custom* function so that I can 
call e.g.

analyser.fletcherMunsonModify(data).

I had already got almost as far as these examples, and in every case 
there was a call to some API function, but there was never a call to a 
custom function nor any hint of how to create one?

THAT is my problem. All this is about how to use what is provided, but I 
want to *extend* what is provided?




-- 
The New Left are the people they warned you about.

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How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-23 12:10 +0000
  Re: How hard can it be? Audio processing JJ <jj4public@gmail.com> - 2021-03-23 21:01 +0700
    Re: How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-23 17:17 +0000
      Re: How hard can it be? Audio processing JJ <jj4public@gmail.com> - 2021-03-24 23:16 +0700
        Re: How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-24 17:48 +0000
  Re: How hard can it be? Audio processing John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-24 18:38 +0000
    Re: How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-24 20:03 +0000
  Re: How hard can it be? Audio processing "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-24 18:01 -0700
    Re: How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-25 07:39 +0000
      Re: How hard can it be? Audio processing The Natural Philosopher <tnp@invalid.invalid> - 2021-03-25 07:50 +0000
        Re: How hard can it be? Audio processing "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-25 06:10 -0700

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