Comments on: Decibel metering from an iPhone audio unit

By: Halle

Halle — Thu, 03 Jan 2013 09:49:33 +0000

Hi Pier,

You are correct, I’ve edited the code in the post. Thanks for catching that!

By: Pier

Pier — Tue, 01 Jan 2013 07:26:48 +0000

Thanks for this… trying to figure it out.

There’s a typo here, no?
if((sampleDB == sampleDB) && (sampleDB = -DBL_MAX))

should be

if((sampleDB == sampleDB) && (sampleDB != -DBL_MAX))

By: Halle

Halle — Thu, 08 Nov 2012 15:56:32 +0000

Hi Waruna,

-74.0 means no input at all. So, you only need to troubleshoot why there is no rendered content in the buffers that are in your callback. All Audio Unit and Audio Session code has a method of error checking (including the buffer callback), so log that error checking code and it should tell you what is happening.

By: Waruna

Waruna — Thu, 08 Nov 2012 15:42:58 +0000

Hi,
Thanks for your resource full article . However when tired this example i always get -74.0 values. Do you what could be the reason for this.
I used recordingCallback function instead of AudioUnitRenderCallback could this be the problem?
Appreciate your answer or any suggestion.

By: Halle

Halle — Mon, 27 Aug 2012 21:45:04 +0000

Hi Ants,

I’d guess that you’re getting unexpected results because of a different input besides a signed 16-bit integer using the full range of samples that this assumes. Since you’re getting floats out, am I correct that your input is a float value?

By: Ants

Ants — Mon, 27 Aug 2012 21:39:13 +0000

Hey Halle,

A couple of questions. Firstly the if that checks for rational number and isn’t infinite

if((sampleDB == sampleDB) && (sampleDB = -DBL_MAX)) {

Shouldn’t that be sampleDB != -DBL_MAX ? I seem to be getting values of DBOFFSET.

If I change to != then I get values out but the range is really small. I tried changing DBOFFSET to -94 however all that did was change the offset (DUH). In my case it seems to be around -9.7 with only slight variation between -10 & -9.6. Is that the low pass filter that is having this effect?

Thanks Ants

By: Halle

Halle — Wed, 06 Jun 2012 13:04:17 +0000

Hiya Thom,

Pitch detection is going to be a little outside of the topic of this blog post, but here is a good SO thread that should get you started and then some: http://stackoverflow.com/questions/7623166/avaudio-detect-note-pitch-etc-iphone-xcode-objective-c

By: thom

thom — Wed, 06 Jun 2012 12:57:07 +0000

Hello hale,

Ive readed true out all the comments. But one thing I just cant figure out. If I want the meter to show me between 400 and 500 Hz what is the best way to get to work with this. The purpose of this is so you can tune instruments with this meter. I hope you still read this topic.

Thanks,
Thom

By: Halle

Halle — Wed, 02 May 2012 07:06:05 +0000

In reply to Tim.

It has a role that is explained in the comments. It’s a quick way of throwing out any NaN values that might come through for unforeseen reasons. Here’s another example for you: http://stackoverflow.com/a/2109282/119717

By: Tim

Tim — Wed, 02 May 2012 02:00:31 +0000

In the above code the condition (sampleDB == sampleDB) should always be true and unnecessary.

Thanks a bunch for sharing this code!