I'm trying to fill an AVAudioPCMBuffer programmatically in Swift to build a metronome. This is the first real app I'm trying to build, so it's also my first audio app. Right now I'm experimenting with different frameworks and methods of getting the metronome looping accurately.
I'm trying to build an AVAudioPCMBuffer with the length of a measure/bar so that I can use the .Loops option of the AVAudioPlayerNode's scheduleBuffer method. I start by loading my file(2 ch, 44100 Hz, Float32, non-inter, *.wav and *.m4a both have same issue) into a buffer, then copying that buffer frame by frame separated by empty frames into the barBuffer. The loop below is how I'm accomplishing this.
If I schedule the original buffer to play, it will play back in stereo, but when I schedule the barBuffer, I only get the left channel. As I said I'm a beginner at programming, and have no experience with audio programming, so this might be my lack of knowledge on 32 bit float channels, or on this data type UnsafePointer<UnsafeMutablePointer<float>>. When I look at the floatChannelData property in swift, the description makes it sound like this should be copying two channels.
var j = 0
for i in 0..<Int(capacity) {
barBuffer.floatChannelData.memory[j] = buffer.floatChannelData.memory[i]
j += 1
}
j += Int(silenceLengthInSamples)
// loop runs 4 times for 4 beats per bar.
edit: I removed the glaring mistake i += 1, thanks to hotpaw2. The right channel is still missing when barBuffer is played back though.
Unsafe pointers in swift are pretty weird to get used to.
floatChannelData.memory[j] only accesses the first channel of data. To access the other channel(s), you have a couple choices:
Using advancedBy
// Where current channel is at 0
// Get a channel pointer aka UnsafePointer<UnsafeMutablePointer<Float>>
let channelN = floatChannelData.advancedBy( channelNumber )
// Get channel data aka UnsafeMutablePointer<Float>
let channelNData = channelN.memory
// Get first two floats of channel channelNumber
let floatOne = channelNData.memory
let floatTwo = channelNData.advancedBy(1).memory
Using Subscript
// Get channel data aka UnsafeMutablePointer<Float>
let channelNData = floatChannelData[ channelNumber ]
// Get first two floats of channel channelNumber
let floatOne = channelNData[0]
let floatTwo = channelNData[1]
Using subscript is much clearer and the step of advancing and then manually
accessing memory is implicit.
For your loop, try accessing all channels of the buffer by doing something like this:
for i in 0..<Int(capacity) {
for n in 0..<Int(buffer.format.channelCount) {
barBuffer.floatChannelData[n][j] = buffer.floatChannelData[n][i]
}
}
Hope this helps!
This looks like a misunderstanding of Swift "for" loops. The Swift "for" loop automatically increments the "i" array index. But you are incrementing it again in the loop body, which means that you end up skipping every other sample (the Right channel) in your initial buffer.
I have a video sequence, lets say seq.mp4. This sequence consists of frames f_1,f_2,...,f_n and I want to reencode the sequence using ffmpeg such that the new sequence consists only of a subset of frames, in particular, the new sequence shall consist only of the frames f_(u*k), where u=1,...,m and m maximal such that k*m <= n. Here, k >=1 is a natural number.
How can I do that using ffmpeg ?
So in Matlab I would do the following:
[str_file,str_path] = uigetfile('*','choose video file');
filename_video_in=fullfile(strcat(str_path,str_file));
sFrames= newid('Sub Frames','Subsequence of Frames',1);
k=str2num(sFrames{1});
tmpFolder=tempname;
mkdir(tmpFolder);
video_in=VideoReader(filename_video_in);
for frame_idx=1:video_in.NumberOfFrames
if mod(frame_idx,k) == 0
img=read(video_in,frame_idx);
fileNumber=frame_idx / k;
imwrite(img,fullfile(tmpFolder,sprintf('img%d.jpg',fileNumber)));
end
end
filename_video_out=strcat(filename_video_in(1:end-4),'_',num2str(k),'- th_frame.',filename_video_in(end-3:end));
video_out=VideoWriter(filename_video_out);
open(video_out);
images=dir(fullfile(tmpFolder,'*.jpg'));
images={images.name}';
images=sort_nat(images,'ascend');
for frame_idx = 1:length(images)
img=imread(fullfile(tmpFolder,images{frame_idx}));
writeVideo(video_out,img);
end
close(video_out);
rmdir(tmpFolder,'s');
I have the following problem:
I have over 20 different models which I want to simulate one after another but I want to change the simulation directory each time.
Right now I'm manually changing directory after each simulation (from ./ModelOne to ./ModelTwo) and I'd like to know if there's a way to change it automatically when I initialize or translate the new model.
Regards
Nev
the best way is to write a script I think:
pathOfSave = {"E:\\work\\modelica\\SimulationResult\\Model1\\","E:\\work\\modelica\\SimulationResult\\Model2\\"};
nbSim = 2;
pathOfMod = { "MyModel.",
"MyModel.};
modelsToSimulate = { ""Model1" ,
"Model2"};
//If equdistant=true: ensure that the same number of data points is written in all result files
//store variables at events is disabled.
experimentSetupOutput(equdistant=false, events=false);
//Keep in the plot memory the last nbSim results
experimentSetupOutput(equdistant=false, events=false);
for i in 1:nbSim loop
//delete the result file if it already exists
Modelica.Utilities.Files.removeFile(pathOfSave + modelsToSimulate[i]);
//translate models
translateModel(pathOfMod[i]+modelsToSimulate[i]);
// simulate
simulateModel(
pathOfMod[i]+modelsToSimulate[i],
method="dassl",
stopTime=186350,
numberOfIntervals=nbOfPoi,
resultFile=pathOfSave + modelsToSimulate[i]);
end for;
You can also put the command cd("mynewpath") in the initial algorithm section, if you want it tobe attached to the model.
model example
Real variable;
protected
parameter String currDir = Modelica.Utilities.System.getWorkDirectory();
initial algorithm
cd("C:\\Users\\xxx\\Documents\\Dymola\\MyModelFolder");
equation
variable = time;
when terminal() then
cd(currDir);
end when;
end example;
In any case you can find all commands of dymola in the manual one under the section "builtin commands".
I hope this helps,
Marco
Is there a way to have a MATLAB timer pass different data on each subsequent call to the timer function? My goal is to cycle through intervals at a fixed rate, and the pause function inside a loop is not precise enough.
I have workng MATLAB code that uses a for loop to send data via serial ports, then wait a specified time before the next iteration of the loop. The serial communication varies in speed, so if I specify 300 seconds as the period, the loop actually executes every 340-360 seconds. Here is the existing code:
clear all;
testFile = input('What is the name of the test data file (with extension): ', 's');
measurementData = csvread(testFile);
intervalDuration = input('What is the measurement change period (seconds): ');
intervalNumber = size(measurementData,2);
% Set up the COM PORT communication
sensorComPort = [101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120];
controllerComPort = [121,122,123,124];
for j=1:intervalNumber
tic
fprintf('\nInterval # %2d\n',rem(j,24));
sensorMeasurementPS = [measurementData(1,j),measurementData(2,j),measurementData(3,j),measurementData(4,j),measurementData(5,j), measurementData(6,j),measurementData(7,j),measurementData(8,j),measurementData(9,j),measurementData(10,j), measurementData(11,j),measurementData(12,j),measurementData(13,j),measurementData(14,j),measurementData(15,j), measurementData(16,j),measurementData(17,j),measurementData(18,j),measurementData(19,j),measurementData(20,j)];
serialSensorObj = startsensorPSWithoutReset(sensorComPort, sensorMeasurementPS);
serialSensorObj = changeMeasurement(serialSensorObj, sensorMeasurementPS);
rc = stopsensorPS(serialSensorObj);
controllerMeasurementPS = [measurementData(21,j),measurementData(22,j),measurementData(23,j),measurementData(24,j)];
serialControllerObj = startControllerPSWithoutReset(controllerComPort, controllerMeasurementPS);
serialControllerObj = changeMeasurement(serialControllerObj, controllerMeasurementPS);
rc2 = stopControllerPS(serialControllerObj);
pause(intervalDuration);
t = toc;
fprintf('Elapsed time = %3.4f\n',t);
end
clear serialSensorObj;
clear serialControllerObj;
The serial functions are specified in other files and they are working as intended.
What I need to do is have the serial communication execute on a more precise 5-minute interval. (The actual timing of the commands inside the interval will still vary slightly, but the commands will kick off every 5 minutes over the course of 24 hours. The current version loses time and gets out of sync with another system that is reading the measurements I'm setting by serial port.)
My first thought is to use a MATLAB timer with the fixedRate execution mode, which queues the function at fixed intervals. However, it doesn't appear that I can send the timer function different data for each interval. I thought about having the timer function change a counter in the workspace, similar to j in my existing for loop, but I know that having functions interact with the workspace is not recommended.
Here's what I've come up with so far for the timer method:
function [nextJ] = changeMeasurement_fcn(obj,event,j,sensorComPort,controllerComPort)
tic
fprintf('\nInterval # %2d\n',rem(j,24));
sensorMeasurementPS = [measurementData(1,j),measurementData(2,j),measurementData(3,j),measurementData(4,j),measurementData(5,j), measurementData(6,j),measurementData(7,j),measurementData(8,j),measurementData(9,j),measurementData(10,j), measurementData(11,j),measurementData(12,j),measurementData(13,j),measurementData(14,j),measurementData(15,j), measurementData(16,j),measurementData(17,j),measurementData(18,j),measurementData(19,j),measurementData(20,j)];
serialSensorObj = startSensorPSWithoutReset(sensorComPort, sensorMeasurementPS);
serialSensorObj = changeMeasurement(serialSensorObj, sensorMeasurementPS);
rc = stopSensorPS(serialSensorObj);
controllerMeasurementPS = [measurementData(21,j),measurementData(22,j),measurementData(23,j),measurementData(24,j)];
serialControllerObj = startControllerPSWithoutReset(controllerComPort, controllerMeasurementPS);
serialControllerObj = changeMeasurement(serialControllerObj, controllerMeasurementPS);
rc2 = stopControllerPS(serialControllerObj);
t2 = toc;
fprintf('Elapsed time = %3.4f\n',t2);
and this is how I would call it from the main m file:
t = timer('TimerFcn',#changeMeasurement,'ExecutionMode','fixedRate','period',intervalDuration);
% then I need some code to accept the returned nextJ from the timer function
This feels a bit sloppy so I'm hoping there's a built-in way to have a timer cycle through a data set.
Another idea I had was to keep the for loop but change the pause function to use a value calculated based on how much time would add up to 5 minutes for the iteration.
To summarize my question:
a) Can I have a timer pass different data to the timer function on each iteration?
b) Is that a good way to go about cycling through the intervals in my data on a precise 5-minute interval?
Thanks!
I stumbled on this page: http://www.mathworks.com/company/newsletters/articles/tips-and-tricks-simplifying-measurement-and-timer-callbacks-with-nested-functions-new-online-support-features.html
and learned that timer callback functions can be nested inside other functions (but not regular scripts).
Using that information, I cut my scenario to the basics and came up with this code:
function timerTestMain_fcn
testFile = input('What is the name of the test data file (with extension): ', 's');
testData = csvread(testFile);
intervalDuration = input('What is the voltage change period (seconds): ');
intervalNumber = size(testData,2);
t = timer('ExecutionMode','fixedRate','period',intervalDuration,'TasksToExecute',intervalNumber);
t.TimerFcn = {#timerTest_fcn};
start(t);
wait(t);
delete(t);
function timerTest_fcn(obj,event)
tic
event_time = datestr(event.Data.time);
interval_id = t.TasksExecuted;
data_value = testData(1,interval_id);
txt1 = 'Interval ';
txt2 = num2str(interval_id);
txt3 = ' occurred at ';
txt4 = ' with data value of ';
txt5 = num2str(data_value);
msg = [txt1 txt2 txt3 event_time txt4 txt5];
disp(msg)
t2 = toc;
fprintf('Elapsed time = %3.4f\n',t2);
end
end
The test data file it requests must be a csv containing a row vector. For example, you could put the values 11,12,13,14,15 across the first row of the csv. The output message would then say 'Interval 1 occurred at [time] with data value of 11', 'Interval 2 occurred at [time] with data value of 12', etc.
The key is that by nesting the functions, the timer callback can reference both the test data and the timer attributes contained in the outer function. The TasksExecuted property of the timer serves as the counter.
Thanks to anyone who thought about my question. Comments welcome.
I used wavread() to read in 3 wave files:
[wave_1 f1]=wavread(s1);
[wave_2 f2]=wavread(s2);
[wave_3 f3]=wavread(s3);
where s1,s2,s3 are the paths for the wave files. The problem is that they are played all at once. How can I play the first, then the second, then the third one after the another?
To play the files sequentially, use the playblocking function. Here is what your code would look like:
[wave_1 f1] = wavread(s1);
[wave_2 f2] = wavread(s2);
[wave_3 f3] = wavread(s3);
player1 = audioplayer(wave_1, f1);
playblocking(player1);
player2 = audioplayer(wave_2, f2);
playblocking(player2);
player3 = audioplayer(wave_3, f3);
playblocking(player3);