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Re: TPAC F2F and Spec Proposals

From: Chris Rogers <crogers@google.com>
Date: Tue, 18 Oct 2011 10:36:43 -0700
Message-ID: <CA+EzO0kj+qC+QEZWU9dztB2B-RXH5F2sXigsfdZ2h6QU1e+niQ@mail.gmail.com>
To: Jussi Kalliokoski <jussi.kalliokoski@gmail.com>, public-audio@w3.org
On Mon, Oct 17, 2011 at 11:28 PM, Jussi Kalliokoski <
jussi.kalliokoski@gmail.com> wrote:

> On Tue, Oct 18, 2011 at 3:47 AM, Chris Rogers <crogers@google.com> wrote:
>
>>
>>
>> On Mon, Oct 17, 2011 at 4:23 PM, Olli Pettay <Olli.Pettay@helsinki.fi>wrote:
>>
>>> On 10/14/2011 03:47 AM, Robert O'Callahan wrote:
>>>
>>>  The big thing it doesn't have is a library of native effects like the
>>>> Web Audio API has, although there is infrastructure for specifying named
>>>> native effects and attaching effect parameters to streams. I would love
>>>> to combine my proposal with the Web Audio effects.
>>>>
>>>
>>>
>>> As far as I see Web Audio doesn't actually specify the effects in any
>>> way, I mean the algorithms, so having two implementations to do the
>>> same thing would be more than lucky. That is not, IMO, something we
>>> should expose to the web, at least not in the audio/media core API.
>>>
>>
>> I'm a bit perplexed by this statement.  The AudioNodes represent
>> established audio building blocks used in audio engineering for decades.
>>  They have very mathematically precise algorithms.  Audio engineering and
>> computer music theory has a long tradition, and has been well studied.
>>
>> Chris
>>
>
> I have to display my ignorance here, as I've yet to see a resource where
> you'd have all these effects and their algorithms defined universally. I've
> seen a lot of different implementations and even more algorithms for doing
> these things, especially filters and reverbs. I haven't heard of a single
> universally accepted algorithm for reverberation or spatialization. Makes
> sense to say that for example a gain effect is standard, but even then
> there's logarithmic gain effects and linear gain effects. The only things
> that stand as standards in my mind are FFT and various window functions,
> which aren't effects per se. Chris, maybe you can point us to a reference
> where these effects are in fact defined in detail?
>
> Jussi
>

Convolution [1] [2] is the technique used for reverberation.  It's defined
with mathematical precision and allows a practically infinite number of
reverberation (and other special effects) depending on the impulse response
file used.  Given a specific impulse response it generates an exact effect.
 For gain effects, the AudioGainNode can have its gain adjusted according to
standard linear/log curves, or with completely arbitrary curves (which are
precisely defined as values in an ArrayBuffer).

Chris

[1] http://en.wikipedia.org/wiki/Convolution
[2] http://en.wikipedia.org/wiki/Convolution_reverb
Received on Tuesday, 18 October 2011 17:37:15 GMT

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