I’m trying to create a kick drum sound that must sound exactly the same when looped at different tempi. The implementation below sounds exactly the same when repeated once every second, but it sounds to me like every other kick has a higher pitch when played every half second. It’s like there is a clipping sound or something.
var context = new AudioContext();
function playKick(when) {
var oscillator = context.createOscillator();
var gain = context.createGain();
oscillator.connect(gain);
gain.connect(context.destination);
oscillator.frequency.setValueAtTime(150, when);
gain.gain.setValueAtTime(1, when);
oscillator.frequency.exponentialRampToValueAtTime(0.001, when + 0.5);
gain.gain.exponentialRampToValueAtTime(0.001, when + 0.5);
oscillator.start(when);
oscillator.stop(when + 0.5);
}
for (var i = 0; i < 16; i++) {
playKick(i * 0.5); // Sounds fine with multiplier set to 1
}
Here’s the same code on JSFiddle: https://jsfiddle.net/1kLn26p4/3/
Not true; oscillator.start will begin the phase at 0. The problem is that you're starting the "when" parameter at zero; you should start it at context.currentTime.
for (var i = 0; i < 16; i++) {
playKick(context.current time + i * 0.5); // Sounds fine with multiplier set to 1
}
The oscillator is set to start at the same time as the change from the default frequency of 440 Hz to 150 Hz. Sometimes this results in a glitch as the transition is momentarily audible.
The glitch can be prevented by setting the frequency of the oscillator node to 150 Hz at the time of creation. So add:
oscillator.frequency.value = 150;
If you want to make the glitch more obvious out of curiosity, try:
oscillator.frequency.value = 5000;
and you should be able to hear what is happening.
Updated fiddle.
EDIT
In addition the same problem is interacting with the timing of the ramp. You can further improve the sound by ensuring that the setValueAtTime event always occurs a short time after playback starts:
oscillator.frequency.setValueAtTime(3500, when + 0.001);
Again, not perfect at 3500 Hz, but it's an improvement, and I'm not sure you'll achieve sonic perfection with Web Audio. The best you can do is try to mask these glitches until implementations improve. At actual kick drum frequencies (e.g. the 150 Hz in your original Q.), I can't tell any difference between successive sounds. Hopefully that's good enough.
Revised fiddle.
Related
When I start up my game it stays around 95-101 rapidly changing, in between all of those numbers.. but when I open up the stats bar I'm getting upper 200's low 300's
so wondering why that is still new to c# so be easy on me lol. heres the code
thanks in advance as always ^_^.
float deltaTime = 0.0f;
void Update()
{
deltaTime += (Time.deltaTime - deltaTime) * 0.1f;
}
void OnGUI()
{
int w = Screen.width, h = Screen.height;
GUIStyle style = new GUIStyle ();
Rect rect = new Rect (0, 0, w, h * 2 / 100);
style.alignment = TextAnchor.UpperRight;
style.fontSize = h * 2 / 100;
style.normal.textColor = new Color (255.0f, 255.0f, 255.0f, 1.0f);
float msec = deltaTime * 1000.0f;
float fps = 1f / deltaTime;
string text = string.Format ("({1:0.} fps)", msec, fps);
GUI.Label (rect, text, style);
}
}
In order to display a meaningful FPS rate you need to measure how many frames were rendered over a constant period of time, for example one second. Then only after that period do you display the calculated value on screen. This will provide for an average frames per second as opposed to an instantaneous frames per second, the latter of which is not particularly useful in most cases as it leads to widely fluctuating values.
Code
First define some fields:
DateTime _lastTime; // marks the beginning the measurement began
int _framesRendered; // an increasing count
int _fps; // the FPS calculated from the last measurement
Then in your render method you increment the _framesRendered. You also check to see if one second has elapsed since the start of the period:
void Update()
{
_framesRendered++;
if ((DateTime.Now - _lastTime).TotalSeconds >= 1)
{
// one second has elapsed
_fps = _framesRendered;
_framesRendered = 0;
_lastTime = DateTime.Now;
}
// draw FPS on screen here using current value of _fps
}
Cross-technology
It should be pointed out that the above code makes no particular use of Unity whilst still being reasonably accurate and is compatible with many frameworks and APIs such as DirectX; OpenGL; XNA; WPF or even WinForms.
When I start up my game it stays around 95-101 rapidly changing, in between all of those numbers.. but when I open up the stats bar I'm getting upper 200's low 300's
The ASUS VG248QE is 1ms and the max it can do is 144Hz so it is unlikely you are getting "upper 200's low 300's". FPS is meaningless when VSYNC is turned off on a non-GSYNC monitor. Is your VSYNC turned on?
In Unity, FPS is equivalent to number of Updates that occur in 1 second. This is because Update() is called every Time.deltaTime seconds.
InvokeRepeating method
You can also use InvokeRepeating to implement your own FPS counter while using only integers, like this:
private int FrameCounter = 0;
private int Fps = 0;
void Start()
{
InvokeRepeating("CountFps", 0f, 1f);
}
void Update()
{
FrameCounter++;
}
private void CountFps()
{
Fps = FrameCounter;
FrameCounter = 0;
}
Then just display the Fps variable in the OnGUI() method. Using this method, your Fps value will get updated every second; if you want more frequent updates, change the last argument of InvokeRepeating call and then adjust the Fps calculation accordingly.
Note, however, that InvokeRepeating takes Time.timeScale into account, so e.g. if you pause the game with Time.timeScale = 0f; the counter will stop updating until you unpause the game.
FixedUpdate method
Another approach is to count the FPS in FixedUpdate() method instead of OnGUI() or Update(). This gets called every Time.fixedDeltaTime seconds which is always the same, no matter what. The value of Time.fixedDeltaTime can be set globally for the project via menu Edit->Project Settings->Time, item Fixed Timestep.
In this case, you would count frames the same way (in Update), but update your FPS counter in FixedUpdate - which is basically the same as calling you own method with InvokeRepeating("CountFps", 0f, 0.02f) (0.02f being a typical Time.fixedDeltaTime value, but this depends on your project settings as per above).
Conclusion
Most of the time, you won't need to update the displayed FPS that often, so I personally like to use the InvokeRepeating method and 1 second intervals.
OnGUI function is called at las twice per frame (sometimes more). You are calculating your "FPS" inside OnGUI so it will almost never be accurate.
Defining :
deltaTime += (Time.deltaTime - deltaTime) * 0.05f;
will bring your FPS values closest to real but it will not be accurate if you calc it on OnGUI method.
I guess (not sure) that you should use FixedUpdate() instead of OnGUI() to calc your FPS. (also you don't need to change your deltaTime to multiply by 0.05f if you use FixedUpdate)
I'm trying to present a 4Hz flickering stimuli in PsychToolbox for 5 seconds followed by a 500Hz tone. Does anyone have an idea of how to do this? I've been using the vbl or screen refresh rate to calculate the flicker frequency but I'm not sure if I'm on the right track at all. I also have no idea how to present an auditory stimuli in PTB (I tried the sound function already). Any help is greatly appreciated!
I'm not sure about sound presentation in PTB (I've never done it), but you seem to be on the right track for the flicker frequency.
The way I do it is to determine the screen refresh rate, divide the total length of time you want the stimulus presented by this refresh rate (this will give you the number of frames that will be drawn during this time), and then have a frame counter that increases by 1 after every flip. You can then use this frame counter to switch commands on or off.
A minimal example (randomly changes the background colour at 4Hz for 5 seconds):
[w, wRect]=Screen('OpenWindow', 0);
MaxTime = 5; %Set maximum time for all stimuli to be presented in seconds
Hz = 4; %Set Hz for stimulus flicker
Screen('Flip',w);
Frametime=Screen('GetFlipInterval',w); %Find refresh rate in seconds
FramesPerFull = round(5/Frametime); % Number of frames for all stimuli
FramesPerStim = round((1/Hz)/Frametime); %Number of frames for each stimulus
StartT = GetSecs; %Measure start time of session
Framecounter = 0; %Frame counter begins at 0
while 1
if Framecounter==FramesPerFull
break; %End session
end
if ~mod(Framecounter,FramesPerStim)
randomcolour = rand(1, 3)*255; %Change background stimulus colour
end
Screen('FillRect', w, randomcolour, wRect);
Screen('Flip',w);
Framecounter = Framecounter + 1; %Increase frame counter
end
EndT = GetSecs; %Measure end time of session
Screen('CloseAll');
EndT - StartT %Shows full length of time all stimuli were presented
The timing precision will depend on your particular refresh rate.
Hope this helps!
I have built an emulated Analog VU Meter for a recording app and have everything hooked up properly and working the way I expect except for one aspect. If you watch this 13-second video of the VU meter in action, you will see that the needle bounces all over the place and is not really what would happen in a real VU meter. For an example of what I am looking for, try out the Apple "Voice Memos" app and see.
My logic so far is easy:
#define VU_METER_FREQUENCY 1.0/5.0
- (void)someMethod {
_updateTimer = [NSTimer
scheduledTimerWithTimeInterval:VU_METER_FREQUENCY
target:self
selector:#selector(_refresh)
userInfo:nil
repeats:YES];
}
- (void)_refresh {
// if we have no queue, but still have levels, gradually bring them down
if (_delegate == nil) {
CFAbsoluteTime thisFire = CFAbsoluteTimeGetCurrent();
// calculate how much time passed since the last draw
CFAbsoluteTime timePassed = thisFire - _peakFalloffLastFire;
needleValue = needleValue - timePassed * VU_METER_LEVEL_FALL_OFF_PER_SECOND;
if (needleValue < VU_METER_MIN_DB) {
needleValue = VU_METER_MIN_DB;
TT_INVALIDATE_TIMER(_updateTimer);
}
_peakFalloffLastFire = thisFire;
} else {
prevNeedleValue = needleValue;
needleValue = [_delegate currentDB];
}
[self updateNeedle];
}
- (void)updateNeedle {
[UIView beginAnimations:nil context:NULL]; // arguments are optional
[UIView setAnimationDuration:VU_METER_FREQUENCY];
[UIView setAnimationCurve:(needleValue > prevNeedleValue ? UIViewAnimationCurveEaseOut : UIViewAnimationCurveEaseIn)];
CGFloat radAngle = [self radianAngleForValue:needleValue];
self.needle.transform = CGAffineTransformMakeRotation(radAngle);
[UIView commitAnimations];
}
Basically, I setup a timer to run at VU_METER_FREQUENCY and update the needle rotation using a UIView animation with easing that is preferential to keep the needle higher. I am looking for a way to adjust this somehow to provide a smoother needle, with my benchmark being as close as possible to Apple's analog VU Meter. To get the needleValue, I am using AudioQueue's mAveragePower and querying it every time currentDB is called. How can I smooth this?
One thing I would suggest is changing this.
#define VU_METER_FREQUENCY 1.0/5.0
That says update 5x a second, the issue is that I think apple will hold 0.2s of samples, so you really are getting an average of the sounds, hence the meter is not really following the highs and lows of the sounds but more of a lower average.
I think this setting can go as high as 1.0/60 (60hz).
As for making the meter smooth, that is a little tricker.
You could do something like this.
Create an array that holds 7-8 values.
every time you get a reading, add it to the array and pop the 7th value of (eg only hold the last seven values.
Find the average of the array (sum the array / divide by the number of elements in the array.
Display this average.
So its a bit like filling up a pipe, and once you stop filling it will take some time for it to empty and needle will slowly fall down.
OR you could only allow the needle to fall down only so much every cycle.
Lets say the needle swings be 0 (lowest value) and 1 (highest value far right hand side).
Lets also say you sample at 20hz (20x times a second).
Every time you update the position only allow the needle to rise say 0.1 of a value max and fall only 0.05 of value.
you could do something like this and play with the values to get it nice and smooth.
if newValue>currentMeterValue
currentMeterValue = Min(currentMeterValue + 0.1, newValue);
else
currentMeterValue = Max(currentMeterValue - 0.05, newValue);
OR
You simply move the meter at a rate proportionally to the distance between each value (this should smooth it nicely) and actually be close to real meter with a spring pushing against the needle which is powered by an electromagnet.
currentMeterValue += (newValue - currentMeterValue)/4.0;
According to Wikipedia, the behavior of a VUMeter is defined in in ANSI specification C16.5-1942. The needle full rise and fall time is supposed to be 300 mSec, averaging loudness over that duration.
I would try a 1-pole low-pass filter on the needle angle to approximate that angular rate, and animate the meter manually on a frame-by-frame basis using CADisplayLink based drawRect animation. View animation might not give the same responsiveness.
I'm working off of some of Apple's sample code for mixing audio (http://developer.apple.com/library/ios/#samplecode/MixerHost/Introduction/Intro.html) and I'd like to display an animated spectrogram (think itunes spectrogram in the top center that replaces the song title with moving bars). It would need to somehow get data from the audio stream live since the user will be mixing several loops together. I can't seem to find any tutorials online about anything to do with this.
I know I am really late for this question. But I just found some great resource to solve this question.
Solution:
Instantiate an audio unit to record samples from the microphone of the iOS device.
Perform FFT computations with the vDSP functions in Apple’s Accelerate framework.
Draw your results to the screen using a UIImage
Computing the FFT or spectrogram of an audio signal is a fundamental audio signal processing. As an iOS developer, whether you want to simply find the pitch of a sound, create a nice visualisation, or do some front end processing it’s something you’ve likely thought about if you are at all interested in audio. Apple does provide a sample application for illustrating this task (aurioTouch). The audio processing part of that App is obscured, however, imho, by extensive use of Open GL.
The goal of this project was to abstract as much of the audio dsp out of the sample app as possible and to render a visualisation using only the UIKit. The resulting application running in the iOS 6.1 simulator is shown to the left. There are three components. rscodepurple1 A simple ‘exit’ button at the top, a gain slider at the bottom (allowing the user to adjust the scaling between the magnitude spectrum and the brightness of the colour displayed), and a UIImageView displaying power spectrum data in the middle that refreshes every three seconds. Note that the frequencies run from low to the high beginning at the top of the image. So, the top of the display is actually DC while the bottom is the Nyquist rate. The image shows the results of processing some speech.
This particular Spectrogram App records audio samples at a rate of 11,025 Hz in frames that are 256 points long. That’s about 0.0232 seconds per frame. The frames are windowed using a 256 point Hanning window and overlap by 1/2 of a frame.
Let’s examine some of the relevant parts of the code that may cause confusion. If you want to try to build this project yourself you can find the source files in the archive below.
First of all look at the content of the PerformThru method. This is a callback for an audio unit. Here, it’s where we read the audio samples from a buffer into one of the arrays we have declared.
SInt8 *data_ptr = (SInt8 *)(ioData->mBuffers[0].mData);
for (i=0; i<inNumberFrames; i++) {
framea[readlas1] = data_ptr[2];
readlas1 += 1;
if (readlas1 >=33075) {
readlas1 = 0;
dispatch_async(dispatch_get_main_queue(), ^{
[THIS printframemethod];
});
}
data_ptr += 4;
}
Note that framea is a static array of length 33075. The variable readlas1 keeps track of how many samples have been read. When the counter hits 33075 (3 seconds at this sampling frequency) a call to another method printframemethod is triggered and the process restarts.
The spectrogram is calculated in printframemethod.
for (int b = 0; b < 33075; b++) {
originalReal[b]=((float)framea[b]) * (1.0 ); //+ (1.0 * hanningwindow[b]));
}
for (int mm = 0; mm < 250; mm++) {
for (int b = 0; b < 256; b++) {
tempReal[b]=((float)framea[b + (128 * mm)]) * (0.0 + 1.0 * hanningwindow[b]);
}
vDSP_ctoz((COMPLEX *) tempReal, 2, &A, 1, nOver2);
vDSP_fft_zrip(setupReal, &A, stride, log2n, FFT_FORWARD);
scale = (float) 1. / 128.;
vDSP_vsmul(A.realp, 1, &scale, A.realp, 1, nOver2);
vDSP_vsmul(A.imagp, 1, &scale, A.imagp, 1, nOver2);
for (int b = 0; b < nOver2; b++) {
B.realp[b] = (32.0 * sqrtf((A.realp[b] * A.realp[b]) + (A.imagp[b] * A.imagp[b])));
}
for (int k = 0; k < 127; k++) {
Bspecgram[mm][k]=gainSlider.value * logf(B.realp[k]);
if (Bspecgram[mm][k]<0) {
Bspecgram[mm][k]=0.0;
}
}
}
Note that in this method we first cast the signed integer samples to floats and store in the array originalReal. Then the FFT of each frame is computed by calling the vDSP functions. The two-dimensional array Bspecgram contains the actual magnitude values of the Short Time Fourier Transform. Look at the code to see how these magnitude values are converted to RGB pixel data.
Things to note:
To get this to build just start a new single-view project and replace the delegate and view controller and add the aurio_helper files. You need to link the Accelerate, AudioToolbox, UIKit, Foundation, and CoreGraphics frameworks to build this. Also, you need PublicUtility. On my system, it is located at /Developer/Extras/CoreAudio/PublicUtility. Where you find it, add that directory to your header search paths.
Get the code:
The delegate, view controller, and helper files are included in this zip archive.
A Spectrogram App for iOS in purple
Apple's aurioTouch example app (on developer.apple.com) has source code for drawing an animated frequency spectrum plot from recorded audio input. You could probably group FFT bins into frequency ranges for a coarser bar graph plot.
Problem:
I am plotting a time series. I don't know apriori the minimum & maximum values. I want to plot it for the last 5 seconds of data. I want the plot to automaticaly rescale itself to best fit the data for the past five seconds. However, I don't want the rescaling to be jerky (as one would get by constantly resetting the min & max) -- when it does rescale, I want the rescaling to be smooth.
Are there any existing algorithms for handling this?
Formally:
I have a function
float sample();
that you can call multiple times. I want you to constantly, in real time, plot the last 5 * 60 values to me, with the chart nicely scaled. I want the chart to automatically rescale; but not in a "jerky" way.
Thanks!
You could try something like
float currentScale = 0;
float adjustSpeed = .3f;
void iterate() {
float targetScale = sample();
currentScale += adjustSpeed * (targetScale - currentScale);
}
And lower the adjustSpeed if it's too jerky.