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Re: DelayNode delay timing specifics

From: Ehsan Akhgari <ehsan.akhgari@gmail.com>
Date: Wed, 28 Aug 2013 12:34:41 -0400
Message-ID: <CANTur_4A4Cmd-dyr7AoUEDc=z+onep3xxk=Geo9S3bjOn=dAYw@mail.gmail.com>
To: Karl Tomlinson <karlt+public-audio@karlt.net>
Cc: "public-audio@w3.org" <public-audio@w3.org>
(2) is what Gecko, Blink and WebKit implement, so we should clarify the
spec here.

I'm not sure if this adequately answers your question here.  If it doesn't,
please let me know!


On Fri, Aug 23, 2013 at 12:56 AM, Karl Tomlinson <
karlt+public-audio@karlt.net> wrote:

> When I first read that the DelayNode "delays the incoming audio
> signal by a certain amount", I imagined something like
> (1)     y(t + d(t)) = x(t)
> for input x(t), output y(t) and delay d(t).
> However, I get the impression that delay lines are often
> implemented as
> (2)     y(t) = x(t - d(t)).
> So I think I may have been reading more into the statement above
> than was intended.
> Can we clarify, please, which effect is intended as the effects
> differ for variable delays of noticeable length, and for larger
> rates of change in delay?
> There is some discussion on these two approaches in [1].
> Both use cases sound to me like they could be useful, so may I
> propose specifying equation (2)?
> I propose (2) because, for small rates of change in the delay, (1)
> can be approximated by applying changes in the delay at a later
> time.  It may be much harder to apply changes in the delay at an
> earlier time, if one were to try to use (1) to approximate (2).
> If the rate of change in delay becomes large, then (1) introduces
> amplitude changes and possibly overlaying behaviour, both of which
> may be not easily emulated using (2).  However, I suspect most
> implementations are not likely nor expected to handle large rates
> of change in delay well anyway.
> "When the delay time is changed, the implementation must make the
> transition smoothly, without introducing noticeable clicks or
> glitches to the audio stream" and the easiest way to do this is to
> limit the rate of change in delay.
> [1]
> https://ccrma.stanford.edu/~jos/doppler/Doppler_Simulation_Delay_Lines.html
Received on Wednesday, 28 August 2013 16:36:11 UTC

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