Buffer size - getNumSamples


I am sorry for stupid question but I am beginner and sometimes it’s still difficult for me to find help in https://juce.com/doc/classes
It’s also question in music technology at all.
getNumSamples returns for me 512. I understand it means in the buffer there are 512 samples. But I can’t find the answer how long (in time) is that buffer? I mean, what is actual sample rate of that buffer? How many samples it generates in one second? Is there any command that I can easy check it or even change?
For any help thanks in advance


The AudioBuffer class doesn’t deal with sample rate. The sample rate is determined elsewhere. If you are doing a plugin you can call getSampleRate in the AudioProcessor::processBlock method. (Apparently it’s not reliable to be called from other methods…)

If you are doing a stand alone application, you can get the sample rate from the current AudioIODevice your AudioDeviceManager is using.


great thanks for your reply.
Actually I’ve just made that tutorial: https://www.youtube.com/watch?v=GjNeYI6-uNE&feature=youtu.be

And guy generates simple noise with that code:

void getNextAudioBlock (const AudioSourceChannelInfo& bufferToFill) override
    for (int channel = 0; channel < bufferToFill.buffer->getNumChannels(); ++channel)
        float* const buffer = bufferToFill.buffer->getWritePointer(channel, bufferToFill.startSample);
        for (int sample = 0; sample < bufferToFill.numSamples; ++sample)
            buffer[sample] = ((random.nextFloat() * 2) - 1) * 0.25f;

And now I made a challange for me, to replace buffer[sample] random function with simple sine wave function. So I think it should be something like that:

buffer[sample] = sin((sample / XXX) * 3.14) * 0.25f;

And now I wonder what should be XXX to get for example 60 Hz wave. But to solve that I need to know what is the frequency of those 512 bufferToFill.numSamples. Am I right or not? If yes, how to find that frequency (sample rate)?

Best Regards


Did you check out the example plug-in?



The sample rate is set in prepareToPlay if you need to set it anywhere for any classes inside your plug-in.

Otherwise you can just call getSampleRate()

The calculation would be

double step = F / getSampleRate();
counter += step; 
float y = sin (counter * 2.0 * double_Pi); 

if (counter >= ) 
    counter -= 1.0; 

Where counter is a member variable initialized to zero. You need to use a counter instead of sample number or else you will get pops in between buffers as the phase isn’t guaranteed to be preserved.


but I can’t just call getSampleRate()

When I execute something like that:
std::cout << getSampleRate() << std::endl;

I get error: Use of undeclared identifier ‘getSampleRate’

So maybe I should #include anything in the header?


getSampleRate() is a method of AudioProcessor.
In C++ (any OO language anyway) you need the object to call a method.

It is not a matter of including something, it means, you can call it inside your processBlock() easily, but no point to call it e.g. in MainComponent or anything similar…