This app is the program which measures the frequency response of the audio system.
It oscillate a low frequency signal from the headphone terminal of iPhone, and it receives the response from microphone.
Then, it records a level every oscillation frequency.
Also, it does the Oscilloscope display of the microphone input, and a frequency analysis by FFT.
It connects with the AUX input terminal of the audio system from the headphone output terminal of iPhone.
It adjusts volume beforehand in the volume of iPhone and the volume of the amplifier.
When beginning measurement, the signal which 1/3 octaves changed a frequency into between 20Hz - 20 kHz is output in 3 seconds by the output terminal of iPhone.
The signal which was received from microphone input by iPhone records the last 1 second of 3 seconds as the response level to the frequency.
It repeats this at each frequency and it displays the graph of the frequency response.
It creates this app in the purpose to use signal output from the headphone terminal for the measurement and the test by connecting it with the other equipment.
When using the speaker of iPhone to output the sound signal of the continuation wave continuously, be careful because there is possibility to cause trouble.
Also, when hearing with the headphone, be careful because there is possibility to cause hearing impairments.
[ Usage ]
1. It uses this app by the side direction display which made the right surface of iPhone an underside.
2. This app is composed of four views which are Response, Oscillo, F.F.T., Setup Freq., Setup Disp. and changes each view with the tab which is in the lower part.
3. The "Response" view
The Response view does the graphical representation of the frequency response with the screen which becomes the basics of this app.
The sine wave of the set frequency is output, it receives the response and it does graphical representation when pushing the "Start" button.
The attenuate graph in the right displays a level in 0.1 seconds at the RMS value.
It displays the graph of the frequency response in the left side.
A graph is reduced when doing a pinch in to the upper and lower direction.
It is expanded when there is a pinch out.
The response level of each frequency is displayed in the tabular form when the "List" button becomes valid after measurement beginning and pushes this button.
during oscillation output, it cancels the automatic lock function of iPhone.
4. The "Oscillo" view
The Oscillo view displays the signal which was received with microphone.
The time axis can be adjusted within 0.01 to 0.1 seconds.
The vertical axis displays 32768 ( the 16 bit resolution ) as 1.0 and can adjust among 0.1-1.0.
When pushing the "Hold" button, the wave stops.
5. The "F.F.T." view
The F.F.T. view changes the signal which was received with microphone in FFT and there is graphical representation.
The horizontal axis is a frequency, and the vertical axis is a logarithm display by the level.
It is computing F.F.T. by 1024 pieces of sampling.
It depends and the frequency resolution is about 43 Hz.
6. The "Setup Freq." view
The Setup Freq. view does the following setting about the oscillation output mainly.
7. The "Setup Disp" view
The Setup Disp. view sets mainly about the way of displaying.
[ Requirement ]
1. Because it uses an audio output continuously at this app, be careful of the consumption of the battery.
2. But saying again, When using the speaker of iPhone to output the sound signal of the continuation wave continuously, be careful because there is possibility to cause trouble.
Also, when hearing with the headphone, be careful because there is possibility to cause hearing impairments.
3. This application is usable only in iPhone4 ( iOS later 4.0 ).
