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Re: General Notes on Web Audio API from TPAC

From: Alistair MacDonald <al@signedon.com>
Date: Mon, 28 Nov 2011 16:50:08 -0500
Message-ID: <CAJX8r2m0sGM5v=gxU3i26cFyYpXos4xD3PZX_ZSvaesmvG37Bw@mail.gmail.com>
To: Chris Rogers <crogers@google.com>
Cc: public-audio@w3.org
Wondered what your thoughts were on this?

Al



On Mon, Nov 28, 2011 at 4:47 PM, Raymond Toy <rtoy@google.com> wrote:

>
>
> On Mon, Nov 28, 2011 at 11:39 AM, Alistair MacDonald <al@signedon.com>wrote:
>
>> Hi Group,
>>
>> While working with the Web Audio API at TPAC I was taking some notes. I
>> sent these to Chris Rogers and we started discussing this a few weeks back.
>>
>> Some of the technical discussion may be very useful / interesting to
>> people experimenting with the API, so I'm going to forward the thread to
>> public-audio here.
>>
>> At the bottom of the email I have attached the original notes I sent to
>> Chris.
>>
>> Comments/discussion always welcome,
>>
>>>
>>> P O S S I B L E  -  B U G S
>>> ===========================
>>>
>>>
>>>
>>> AudioParam ...RampToValueAtTime( 0, 0 )
>>> ---------------------------------------
>>>
>>> Exponential ramps do not seem to work properly when starting using
>>> "zero" values.
>>> I would expect to hear the sound ramping in from 0 or out to 0, instead
>>> the
>>> transition appears to be immediate when it reaches the given time. Much
>>> like the
>>> behavior of the setValueAtTime() method.
>>>
>>
>> This is a consequence of the math behind exponential curves.  You can
>> always have an exponentially increasing curve from
>> value1 -> value2
>>
>>
> It's not clear from the webaudio docs what an exponential ramp should do,
> but we could define the ramp to be
>
> value1 + (value2-value1)*(1-exp(-t/C))
>
> This will be an exponential ramp starting at value1 and asymptotically
> approaching value2.
>
> Two major differences:
>
>
>    - 0 is valid starting point.
>    - We never actually reach value2, but just get closer and closer.
>
> Ray
>
>
Received on Monday, 28 November 2011 21:50:37 GMT

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