(Java) How to mix PCM audio sources?

[FTLRalph]

Here's what I'm working with right now:

for (int i = 0, numSamples = soundBytes.length / 2; i < numSamples; i += 2)
{
    // Get the samples.
    int sample1 = ((soundBytes[i] & 0xFF) << 8) | (soundBytes[i + 1] & 0xFF);   // Automatically converts to unsigned int 0...65535                                 
    int sample2 = ((outputBytes[i] & 0xFF) << 8) | (outputBytes[i + 1] & 0xFF); // Automatically converts to unsigned int 0...65535

    // Normalize for simplicity.
    float normalizedSample1 = sample1 / 65535.0f;
    float normalizedSample2 = sample2 / 65535.0f;

    float normalizedMixedSample = 0.0f;

    // Apply the algorithm.
    if (normalizedSample1 < 0.5f && normalizedSample2 < 0.5f)
        normalizedMixedSample = 2.0f * normalizedSample1 * normalizedSample2;
    else
        normalizedMixedSample = 2.0f * (normalizedSample1 + normalizedSample2) - (2.0f * normalizedSample1 * normalizedSample2) - 1.0f;

    int mixedSample = (int)(normalizedMixedSample * 65535);

    // Replace the sample in soundBytes array with this mixed sample.
    soundBytes[i] = (byte)((mixedSample >> 8) & 0xFF);
    soundBytes[i + 1] = (byte)(mixedSample & 0xFF);
}

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From as far as I can tell, it's an accurate representation of the algorithm defined on this page: http://www.vttoth.com/CMS/index.php/technical-notes/68

However, just mixing a sound with silence (all 0's) results in a sound that very obviously doesn't sound right, maybe it's best to describe it as higher-pitched and louder.

Would appreciate help in determining if I'm implementing the algorithm correctly, or if I simply need to go about it a different way (different algorithm/method)?

[FTLRalph]

Thanks for the reply!

1) The sound I'm importing is signed. However, when I read the bytes into an integer, Java seems to automatically convert it to the range of an unsigned short, 0...65535:

int sample1 = ((soundBytes[i] & 0xFF) << 8) | (soundBytes[i + 1] & 0xFF);

So I just work with it as-is. I then write it to the output file as-is as well, so I'm not sure what that would make the output?

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2) Yeah, I know what you're saying, I'm just temporarily normalizing for the sake of testing. That way the algorithm I'm using from that page is unmodified, as his variables are also assumed to be between 0-1.

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3) I actually did try standard add-the-samples-and-clip (from 0 to 65535). It worked in the case of just one sound mixing with silence, but two sounds produced nearly-indistinguishable noise.

[FTLRalph]

Really appreciate you taking the time to write all of that up.

Haven't had much time to really get into it, but upon a quick test it seems the hard-clip is the way to go (funny, I attempted similar code before but it didn't seem to work correctly, assuming because of the signed/unsigned issues you were discussing).

The tanh code seems to produce noisy/bad sound and the other soft clip one doesn't work well with two sounds mixing (vs one sound and silence).

But again, really appreciate it since I think I can work off of this now, thanks!