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Listing 6 ends by scaling the gain factor by 8000 to produce a reasonable audio output level.
Listing 7 examines the sign (positive or negative) of the current value of the sinusoidal function (based on the pulse frequency relative to the center frequency) and uses that information to compute gain factors that will turn one speaker on and turn the other speaker off.
| Listing 7 . Compute the gain for the left and right speakers. |
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if(freq>= centerFreq){
leftGain = gain;rightGain = 0;//switch off the right channel
}else{rightGain = gain;
leftGain = 0;//switch off the left channel}// |
As you learned in an earlier module, given the values that we are using in the AudioFormatParameters01 object, the format requirements for monaural and stereo are shown below. (Note that in both cases, each audio value must be a signed 16-bit value decomposed into a pair of 8-bit bytes.)
For mono, each successive pair of bytes in the melody array must contain one audio value. The element with the lower index must contain the most significant eightbits of the 16-bit audio value.
For stereo, alternating pairs of bytes must each contain one audio value in the same byte order as for mono. One pair of bytes is routed to the left speakerand the other pair of bytes is routed to the right speaker (almost) simultaneously.
Within the four bytes, the pair with the lowest index is routed to the left speaker and the other pair is routed to the right speaker.
You learned how to use the putShort method belonging to an object of the ByteBuffer class to deposit the short data into the byte array in the earlier module titled Jbs2030-A Pure Sinusoidal Tone .
Listing 8 used the information from above to compute the current audio value of the pulse and to deposit it into two consecutive pairs of bytes in the melody array. Note that the putShort method is called twice, once for each channel. Note also that the values of leftGain and rightGain are used to scale each audio value so that it will be emitted from only one of the two stereo speakers.
| Listing 8 . Deposit stereo audio data in the melody file. |
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byteBuffer.putShort((short)(leftGain*Math.sin(2*Math.PI*freq*time)));
byteBuffer.putShort((short)(rightGain*Math.sin(2*Math.PI*freq*time)));}//end for loopreturn melody;
}//end method getMelody//-------------------------------------------------------------------------//
}//end class AudioGraphSinusoidal |
Listing 8 returns a reference to the melody array when the for loop terminates.
Listing 8 also signals the end of the getMelody method and the end of the AudioGraphSinusoidal class.
This module demonstrates one way to control the output levels from the two speakers in a stereo melody. It is not necessary that one speaker be turnedcompletely off and the other speaker turned completely on as is the case here. The relativelevels of the audio outputs from the two speakers can be controlled by adjusting the relative values of the left and right gain values.
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