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Re: two questions about FFT/IFFT

From: Matt Diamond <mdiamond@jhu.edu>
Date: Wed, 13 Apr 2016 10:58:02 -0400
Message-ID: <CADdpXtvwySOGp63HMJ1b1dT8On0v+MBwAMqkhnQYxfw9cSdJGQ@mail.gmail.com>
To: Paul Adenot <padenot@mozilla.com>
Cc: Raymond Toy <rtoy@google.com>, "public-audio@w3.org" <public-audio@w3.org>
Thank you Paul and Nevo for the helpful replies. I think I've got a handle
on it now.

Matt

On Wed, Apr 13, 2016 at 5:15 AM, Paul Adenot <padenot@mozilla.com> wrote:

> Something like this maybe ?
>
> function frequencyForBinIndex(index) {    return (index - 1) *           this.audioContext.sampleRate /           this.analyser.fftSize;}
> Paul.
>
>
>
> On Wed, Apr 13, 2016 at 2:04 AM, Matt Diamond <mdiamond@jhu.edu> wrote:
>
>> Thanks for the reply. This might be a silly question, but is there an
>> equation I can use to reliably calculate the actual frequency range of each
>> bin returned by the analyser? I get an array of decibel values but I don't
>> know exactly what frequencies they correspond to.
>>
>> Matt
>>
>> On Tue, Apr 12, 2016 at 7:32 PM, Raymond Toy <rtoy@google.com> wrote:
>>
>>>
>>>
>>> On Tue, Apr 12, 2016 at 2:24 PM, Matt Diamond <mdiamond@jhu.edu> wrote:
>>>
>>>> 1) Is it possible to do a non-realtime spectral analysis of a
>>>> BufferSource using an AnalyserNode with an OfflineAudioContext?
>>>>
>>>
>>> Yes, but you probably need to use suspend/resume to get correct timing.
>>>
>>>>
>>>> 2) Is it possible for me to use a PeriodicWave to convert an array of
>>>> frequency data from the Analyser Node back into a time-domain waveform? It
>>>> seems like this isn't possible.
>>>>
>>>
>>> Right.  The analyser loses the phase information so you can't get the
>>> original back.
>>>
>>>>
>>>> Basically I'd like to come up with a web-based version of the spectral
>>>> averaging technique that R Luke DuBois employed on Timelapse... averaging
>>>> the spectral content of an entire buffer and then reproducing that content
>>>> as a sustained drone. Is that possible yet with the Web Audio API as it
>>>> currently exists?
>>>>
>>>> Thanks,
>>>> Matt Diamond
>>>>
>>>
>>>
>>
>
Received on Wednesday, 13 April 2016 14:58:32 UTC

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