I am interested in a way to play sounds from specific points in space relative to the user.
Basically I would like to say the user is at point (0,0) and a sound came from (10,10) and then take a sound and send it through some library that plays it, sounding as though it came from the source (10,10). Performance in doing this would be very important.
If it wasn't painfully obvious from reading the question, I have very little experience with audio on any device.
After doing a little research, it seems the options are to use the OpenAL framework which is supported by apple, or essentially roll your own on top of Audio Unit.
There is a 3D Mixer Audio Unit that apple provides, which requires you to develop a lot of understanding of Audio Units.
Then there is OpenAL which is a cross platform audio framework where you can position a "source" and a "listener" and it will compute attenuation and stereo for you.
Both require low level understanding of playing Audio and are not very fun. So I figured I might as well jump all the way in the water and learn about the Audio Units, since I may want to do some more specialized stuff in the future.
This is an easy wrapper for the iOS OpenAL functionality: ObjectAL-for-iPhone
Play around with the example and see if it does what you want.
Related
I'm looking for a way to create a audio bars visualizer similar to this in iOS.
Every white bar will move up and down depending of audio wave. I'm really lost because haven't much experience dealing with audio in Objective-c.
EDIT: What i'm seeking is what Overcast's app does on its visualizer (the group of vertical orange bars on the lower part of the podcast's image)
Anyone can help?
Thanks
EDIT: Thanks to Tomer's answer I finally made it. First I did this tutorial in order to make it all clear. Then I created my own VisualizerView for my project, you can find it in this gist. Maybe is not perfect but it does what I needed to do.
Generally, you have a few options if you want to get an idea of what something sounds like in iOS:
Use the simple AVAudioPlayer audio player, and then use the [audioPlayer averagePowerForChannel:] method to get the avarage audio level for the current moment. Check out this tutorial.
Use the Audio Queue API, which lets you send whatever audio you want to the speaker: You would read audio from your source and fill the buffers with it every time. (If you're reading from a file, use AVAssetReader) This way you always know exactly what waveform you're playing, so you can, for example, calculate its avarage power or process it in other ways like FFT. Then you'd update the bars accordingly.
EDIT: The standard way of doing such a thing is to use the Fast Fourier Transform (FFT) - it extracts frequency information from a sound. Here's a good example of using it on iOS (Apple's guide here). But, of course, to use it you have to know exactly what waveform you're playing every time, so you'd probably want to use a lower-level API such as Audio Queue.
I am recording videos and playing them back using AVFoundation. Everything is perfect except the hissing which is there in the whole video. You can hear this hissing in every video captured from any iPad. Even videos captured from Apple's inbuilt camera app has it.
To hear it clearly, you can record a video in a place as quiet as possible without speaking anything. It can be very easily detected through headphones and keeping volume to maximum.
After researching, I found out that this hissing is made by preamplifier of the device and cannot be avoided while recording.
Only possible solution is to remove it during post processing of audio. Low frequency noise can be removed by implementing low pass filter and noise gates. There are applications and software like Adobe Audition which can perform this operation. This video shows how it is achieved using Adobe Audition.
I have searched Apple docs and found nothing which can achieve this directly. So I want to know if there exists any library, api or open source project which can perform this operation. If not, then how can I start going in right direction because it does looks like a complex task.
Basically i'm gonna be working on an iOS music app which when a song is being played, it shows the fancy Equalizer meter, Something like this but with all the animation of bars going up and down:
After looking into this and not finding enough resource, I really want to carry this as a project perhaps making a web version using j query.
I'm not really asking for specific code, i just want to know how the animation works in general ?
Thanks a million !!!
Checkout the Cocoa Waveform Audio Player Control project. It's a cocoa audio player component which displays the waveform of the audio file.
Also, there is already a lot of questions on this topic:
iOS FFT Accerelate.framework draw spectrum during playback
Using the Apple FFT and Accelerate Framework
iOS FFT Draw spectrum
Animation would be pretty straight forward. It is just animating changes of the height of rectangles.
I am trying do slow motion for my video file along with audio. In my case, I have to do Ramped Slow motion(Gradually slowing down and speeding up
like parabola not a "Linear Slow Motion".
Ref:Linear slow motion :
Ref : Ramped Slow Motion :
What have i done so far:
Used AVFoundation for first three bullets
From video files, separated audio and video.
Did slow motion for video using AVFoundation api (scaletimeRange).Its really working fine.
The same is not working for audio. Seems there's a bug in apple api itself (Bug ID : 14616144). The relevant question is scaleTimeRange has no effect on audio type AVMutableCompositionTrack
So i switched to Dirac. later found there is a limitation with Dirac's open source edition that it doesn't support Dynamic Time Stretching.
Finally trying to do with OpenAL.
I've taken a sample OpenAL program from Apple developer forum and executed it.
Here are my questions:
Can i store/save the processed audio in OpenAl?if its directly not possible with "OpenAl", can it be done with AVFoundation + OpenAL?
Very importantly, how to do slow motion or stretch the time scale with OpenAL? If i know time stretching, i can apply logic for Ramp Slow Motion.
Is there any other way?
I can't really speak to 1 or 2, but time scaling audio can be as easy as resampling. If you have RAW/PCM audio sampled at 48 kHz and want to playback at half speed, resample to 96 kHz and play the audio at 48 kHz. Since you have twice the number of samples it will take twice as long to play. Generally:
scaledSampleRate = (orignalSampleRate / playRate);
or
playRate = (originalSampleRate / scaledSampleRate);
This will effect the pitch of the track, however that may be the desired effect since that behavior is somewhat is expected in "slow motion" audio. There are more advanced techniques that preserve pitch while scaling time. The open source software Audacity implements these algorithms. You could find inspiration there. There are many resources on the web that explain the tradeoffs of pitch shifting vs time stretching.
http://en.wikipedia.org/wiki/Audio_time-scale/pitch_modification
http://www.dspdimension.com/admin/time-pitch-overview/
Another option you may not have considered is muting the audio during slow motion. That seems to be the technique employed by most AV playback utilities. However, depending on your use case, distorted audio does indicate time is being manipulated.
I have applied slow motion on complete video including audio this might help You check this link : How to do Slow Motion video in IOS
I'm a Unity dev and need to help out colleagues with doing this natively in Obj-C. In Unity it's no big deal :
1)samples are stored in memory as a List of float[]
2)A helper function returns float[] of n size for any given sample, at any given offset
3)Another helper function fades the data if needed
4)An AudioClip object is created with the right size to accomodate all cut samples, and is then filled at appropriate offsets.
5)The AudioClip is assigned to a player component(AudioSource).
6)AudioSource.Play(ulong offsetInSamples), plays at a sample accurate time in the future. Looping is also just a matter of setting the AudioSource object's loop parameter.
I would very much appreciate if someone could point me towards the right classes to achieve similar results in Obj-C, for iOS devices. I'm pretty sure a lot of iOS audio newbies would be intersted too. Many thanks in advance!
Gregzo
A good overview of the relevant audio APIs available in iOs is here
The highest level framework that makes sense for patching together audio clips, setting their volume levels, and playing them back in your case is probably AVFoundation.
It will involve creating AVAssets, adding them to AVPlayerItems, possibly putting them into AVMutableCompositions to merge multiple items together and adjust their volumes (audioMix), and them playing them back with AVPlayer.
AVFoundation works with AVAsset, for converting between relevant formats and lower level bytes you'll want to have a look at AudioToolbox (I can't post more than two links yet).
For an somewhat simpler API with less control have a look at AVAudioPlayer. If you need greater control (eg: games - real time / low latency) you might need to use OpenAL for playback.