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Android Sine Wave Synthesis

Part 6 - Using a Scope and Limits

Preceding tutorials in this series:

Tutorials in that series that follow:

Finally, I just want to take a look at the sampled sine wave on a software based oscilloscope and compare the result with the simulated version. To do this I loaded the project onto an Android device as an app and used the freeware version of Visual Analyser 2011 to examine the output. Visual analyser is a fantastic tool and I fully recommend that you download a copy from here . Take a look at the screen shots below.

Outputs from the Oscilloscope

You can see that the fidelity of the wave is very good at 440 Hz as expected from the simulation. At 3400 Hz, which sis the limit of human speech, the fidelity of the wave is still good, but is starting to breakdown.  This is expected as we only have 13 samples per period at a 44100 Hz sample rate. It does, however, compare very well with the simulation. At 10000 Hz, the output starts to resemble a saw tooth wave. This is expected as only have 4 samples per period. Again, though the output resembles the simulated wave very well.

It is clear that there are limits to what can be achieved with a PCM based function generator. The limitations are due to PCM at 44.1 KHz though, rather than the Android device itself.

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