Re: Getting Volume Controls
Re: Getting Volume Controls
- Subject: Re: Getting Volume Controls
- From: Jeff Moore <email@hidden>
- Date: Mon, 20 Sep 2004 12:47:30 -0700
The meter the Sound Prefs panel uses is derived from looking at the
audio data in an IOProc as it goes by.
There are lots of algorithms for extracting useful numbers for making
the meter bounce. Most of the algorithms have to do with calculating
the peak value or average power or some other attribute over a range of
time and then drawing that. The individual algorithms are all tuned to
achieve different results from just making the lights bounce nice (like
QTPlayer) to deep analysis (like Spectrafoo).
This has been discussed here before, so perusing the archives should be
helpful. Plus, I'm sure others on this list wouldn't mind sharing their
experiences on designing good meters or at least point out good
reference material =)
On Sep 20, 2004, at 12:34 PM, bryan wrote:
Thank you, Jeff. I eventually stumbled onto this fact :)
In the system audio settings, where you can select the between
microphone and
line input, there is a "vu meter" that shows the input level. Can you
tell me
the exact calculation used in this level display? Or if it is
possible to get
the system to give me the input level directly?
Quoting Jeff Moore <email@hidden>:
What you are missing is the fact that not all pieces of hardware have
a
master volume control, which is what you are asking about in your
code.
It is quite common for devices, like the built-in hardware on most
Macs, to have individual channel volumes so you would need to ask for
the volume on channel 1 and channel 2 as well as the master channel.
On Sep 18, 2004, at 11:56 AM, bryan wrote:
I am using the Java CoreAudio classes, and I want to be able to read
the
volume on the default input and output devices, but I am running into
problems:
// query for the input device -- succeeds
AudioDevice device = AudioHardware.getDefaultInputDevice();
// create a memory object to hold the Float32
CAMemoryObject propVal = new CAMemoryObject(4,true);
// query for the volume -- fails with
kAudioHardwareUnknownPropertyError
device.getInputProperty
(0,AHConstants.kAudioDevicePropertyVolumeScalar,propVal);
I have also tried to query for kAudioDevicePropertyVolumeDecibels
with
the
same result.
Any idea what I am missing?
Thanks,
Bryan
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Apple
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