how to make audio meter level with avaudiorecorder - iphone

Question

I am trying to create a audio meter level while I am recording the user voice using avaudiorecorder. Can someone help me in that regard?

Answer 1

Actually, the code is pretty straightforward since AVAudioPlayer and AVAudioRecorder have built in methods to get you on your way. My approach was this:
make a repeating call to -updateMeters and the averagePowerForChannel: & peakPowerForChannel: methods and call a delegate method to notify the controlling object
Example:
NSOperationQueue *queue=[[NSOperationQueue alloc] init];
NSInvocationOperation *operation=[[NSInvocationOperation alloc] initWithTarget:self selector:#selector(updateMeter) object:nil];
[queue addOperation: operation];
and
-(void)updateMeter
{
do {
//don't forget:
[recorder updateMeters];
self.averagePower = [recorder averagePowerForChannel:0];
self.peakPower = [recorder peakPowerForChannel:0];
// we don't want to surprise a ViewController with a method call
// not in the main thread
[self.delegate performSelectorOnMainThread: #selector(meterLevelsDidUpdate:) withObject:self waitUntilDone:NO];
[NSThread sleepForTimeInterval:.05]; // 20 FPS
}while(someCondition);
}
If your View Controller implements the meterLevelsDidUpdate: method, you can use this method to update your Level Meter.
create a UIView subclass with a subview that changes its height according to the average or peak value(s). Adjust to taste.

Answer 2

Easy, you can use NSTimer for that:
- (void)startAudioMetering {
self.meterTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(updateAudioMeter)userInfo:nil repeats:YES];
}
- (void)stopAudioMetering {
[self.meterTimer invalidate];
}
- (void)updateAudioMeter { //called by timer
// audioRecorder being your instance of AVAudioRecorder
[self.audioRecorder updateMeters];
self.dBLevel = [self.audioRecorder averagePowerForChannel:0];
}
WARNING: While creating your AVAudioRecorder instance, you have to call meteringEnabled AFTER you call prepareToRecord or record, otherwise it won't updateMeters:
[self.audioRecorder prepareToRecord];
self.audioRecorder.meteringEnabled = YES;

Answer 3

Swift code based on Tom's answer:
NSOperationQueue().addOperationWithBlock({[weak self] in
repeat {
self?.audioRecorder.updateMeters()
self?.averagePower = self?.audioRecorder.averagePowerForChannel(0)
self?.peakPower = self?.audioRecorder.peakPowerForChannel(0)
self?.performSelectorOnMainThread(#selector(DictaphoneViewController.updateMeter), withObject: self, waitUntilDone: false)
NSThread.sleepForTimeInterval(0.05)//20 FPS
}
while (someCondition)
})
Do the meter UI stuff inside func updateMeter(){//UI stuff here}

Answer 4

Its pretty simple,
The values you get in the buffer are positive and negative (this is how the waves work) so if you do the average of that values it will give you a near 0 value.
So what you have to do is just put all values positive (with the Math.abs() function) and then do the avarage, it will return you the sound level.
Hope this helps ;)

Answer 5

You can also use ReactiveCocoa and make use of interval:onScheduler::
Returns a signal that sends the current date/time every interval on scheduler.
Using a single audio channel:
#weakify(self)
RACDisposable *metersDisposable = [[RACSignal // make sure you dispose it eventually
interval:0.1
onScheduler:[RACScheduler scheduler]]
subscribeNext:^(NSDate *) {
#strongify(self)
[recorder updateMeters];
auto averagePower = [recorder averagePowerForChannel:0];
auto peakPower = [recorder peakPowerForChannel:0];
// Inform the delegate or make other use of averagePower and peakPower
}];

Answer 6

I found the answer in following link.
AVMeter for AVPlayer
Though it requires lot of customizations but I feel I will be able to do it.