Re: Peak and averagePowerForChannel are nice, but what about the actual current power?
Re: Peak and averagePowerForChannel are nice, but what about the actual current power?
- Subject: Re: Peak and averagePowerForChannel are nice, but what about the actual current power?
- From: Ochen Kaylan <email@hidden>
- Date: Fri, 15 May 2009 23:39:39 -0500
Thanks Brian.
Ambiguity: You're right. I didn't mean that I needed the power of
1/60th of a second of audio, since many samples are included within
that 1/60th of a second. What I meant was that I only need the actual
power of one sample every 1/60th of a second. There will be plenty of
samples that will not be counted between those single samples every
1/60th of a second. For my needs, that's fine.
Average not spanning multiple buffers: I'm not sure I follow you here.
The only time I'm having a problem with falloff is using the
AVAudioPlayer meter functions. Are you saying that there is a way to
set the falloff time of AVAudioPlayer meter readings? I'm not aware of
one, so if there is, can you point me to where I can find out more
about it? If you're saying that by using AudioQueue, I can limit
falloff, why would I do that if I can access the actual sample levels
and avoid falloffs all together? I don't think I'm following what
you're saying.
Why the need: There are a few different reasons I need the
instantaneous power. The easiest one to explain is waveforms. You
can't draw waveforms with only average or peak power. If the audio is
10 minutes long, but the waveform is only going to be 100 pixels wide,
there's no need to have the instantaneous power of every sample. A few
a second is plenty for that scenario. Do you have any suggestions on
how a waveform can be drawn without digging into the PCM data, mapping
the entire file, averaging the instantaneous powers to fit the display
needs, and rendering it out? I'm fine doing it that way, but that's
not easy on the processor, nor is it terrible quick. Pulling meter
data from an AVAudioPlayer is a snap, if only instantaneous power was
retrievable.
Thanks again for following up on this. I look forward to any thoughts
you might have.
On May 15, 2009, at 5:01 PM, Brian Willoughby wrote:
On May 15, 2009, at 11:50, email@hidden wrote:
I don't need sample-level granularity. 1/60th of a second is fine,
but I need the true level, not an averaged level, and the falloff
is longer than 1/60th of a second.
There is an inherent ambiguity in your request for the instantaneous
power for 1/60th of a second. There are hundreds, if not thousands
of 'instants' in that time period. You need to define whether you
want the largest instantaneous power during that period, or the
average, or the minimum, or the mean, or what. You certainly cannot
update your meter tens of thousands of times per second.
Your best bet is to get the full PCM audio data in your code and
compute your own power, using your own definition. You could design
your averaging so that no state is saved between buffers, and thus
there would be no falloff. That still isn't instantaneous power,
but it's an average power which does not span multiple buffers.
Brian Willoughby
Sound Consulting
P.S. What is this to be used for? Why do you seek instantaneous
power?
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| References: | |
| | >Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Ochen Kaylan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Hamish Allan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Ochen Kaylan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Hamish Allan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: email@hidden) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Hamish Allan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: email@hidden) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Hamish Allan <email@hidden>) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: email@hidden) |
| | >Re: Peak and averagePowerForChannel are nice, but what about the actual current power? (From: Brian Willoughby <email@hidden>) |