CS 3005: Programming in C++

Audio Track Creator (Additional Features)

Introduction

In the previous assignment, you created a program that creates an AudioTrack object and fills it with data, depending on the user’s choice. In this assignment, you will add additional choices for the form of data that can be added to an AudioTrack object.

The two options are sine and sawtooth waves. The sine wave is generated using the std::sin(angle) function from the C++ standard library. An angle must be computed that corresponds to a position on the horizontal axis of the graph.

Given sample_number (the position in the audio track), frequency (how quickly the wave changes), and samples_per_second (the sample rate)

Then: angle = (6.28 * sample_number * frequency) / samples_per_second

The following is a graph for samples_per_second = 1000 over a 1.23 second interval, at frequency = 10.0.

A sawtooth wave also follows a periodic pattern. But, it has straight line edges, that produce a pattern that resembles the teeth of a saw. The

Given: sample_number (the position in the audio track, an unsigned int), frequency (how quickly the wave changes, a double), and samples_per_second (the sample rate, an int)

Then:

• cycle_size = samples_per_second/frequency is how many samples there are per cycle.
• j = sample_number % cycle_size is the how far into the current cycle the current sample is.
• amplitude = -1.0 + (2.0 * j) / (cycle_size - 1) is the amplitude of the sawtooth wave.

Even though frequency is a double, we want cycle_size to be an unsigned int. So, we assign the result of the division into cycle_size and intentionally discard any fractional part of the result. This is necessary because we want a discrete number of samples per cycle.

Now, when we compute j as an unsigned int, the % operator will work find with two integer types as operands.

Finally, amplitude is a double, that is computed from some float and some integer inputs. When (2.0 * j) is computed, j’s value is promoted to double to match the type of 2.0. When the division (2.0 * j) / (cycle_size - 1) happens, the numerator is a double because it’s the result of 2.0 * j. The denominator’s value will be promoted to double to match the type of the numerator. So, the overall computation results in a correct double value.

The following is a graph for samples_per_second = 23 over a 1.34 second interval, at frequency = 5.0.

Assignment

In this assignment, you will update the audio_track_creator program to allow the user to select sine or sawtooth wave data in addition to the ramp options that were made available in the previous assignment.

An example interaction with the program could look like this:

Samples/Second: 1000
Seconds: 1.23
Fill style: sine
Frequency: 10

sample_number,amplitude
0,0
1,0.0627587
2,0.12527
3,0.187287
...
1228,0.988864
1229,0.977574

Another example interaction with the program could look like this:

Samples/Second: 1000
Seconds: 1.23
Fill style: whammy
Fill style 'whammy' is not allowed.

Programming Requirements

Update library-application/ApplicationData.{h,cpp}

ApplicationData Class

Data Members:

• std::vector<double> doubleRegisters; Vector of ‘registers’ to store values for the application. Should be initialized in the constructor to have 5 register slots (size of 5).

public Methods:

• double getDoubleRegister(const unsigned int position) const; Returns the value of the given register. If position is out of range, return -INFINITY.
• void setDoubleRegister(const unsigned int position, const double value); Assigns the value of the given register to the given value. if position is out of range, do nothing.

Update library-commands/audio_track_creator_aux.{h,cpp}

Functions:

• void sine_fill_audio_track(ApplicationData& app_data); Fills the audio track of the given ApplicationData with a sine wave. The formula to get the amplitude at each sample should be as follows: std::sin(angle). angle is computed using the formula described above. samples_per_second is the value previously assigned to the audio track and frequency is the value stored in the ApplicationData’s register 0.
• void sawtooth_fill_audio_track(ApplicationData& app_data); Fills the audio track of the given ApplicationData with a sawtooth waveform. The formula to get the amplitude of the sawtooth wave is described above. The samples_per_second and frequency are found as in sine_fill_audio_track.
• void fill_audio_track(ApplicationData& app_data); This function should be updated to be able to call the new functions above. In both new cases, it should prompt the user for a frequency value which should be stored in register 0 of the ApplicationData to be used inside the new functions. The prompts and error outputs should match the example executions shown above.

Additional Documentation

• sin
• floor
• %, modulo/remainder

Grading Instructions

To receive credit for this assignment:

• your code must be pushed to your repository for this class on GitHub
• all unit tests must pass
• all acceptance tests must pass
• all programs must build, run, and execute as described in the assignment descriptions.

Extra Challenges (Not Required)

• Make a square_fill_audio_track function that fills the audio track with a square wave.
  • Square Wave
• Make a triangle_fill_audio_track function that fills the audio track with a triangle wave.
  • Triangle Wave
• Make a pulse_fill_audio_track function that fills the audio track with a pulse wave. This should prompt the user for an additional value of a duty_cycle. A duty_cycle value of 0.5 should produce a pulse wave identical to your square wave.
  • Pulse Wave

Last Updated 02/04/2025