CODEWITHSUNDEEP
c#naudio
TheBard
TheBard

Reputation: 346

bytes to sbytes and back - C# NAudio

I need to normalize an 8 bit audio .wav file.

I used NAudio to load the file to a byte[]. I successfully converted this to an sbyte[] and recovered the sine bit. I then multiply this array (casting to a float) to get the normalized value (0-255) hard limited.

Now I need to save it back as a byte[] to let NAudio write it. The problem is, if I just cast, 

source[i] = (byte)normalizedFloatArray[i];

The resulting saved .wav looks like this! Ouch.

goofy wave

"goofy wave"

Where might the problem lie?

Upvotes: 3

Views: 220

Answers (2)

Mike Strobel
Mike Strobel

Reputation: 25623

Casting a byte to an sbyte causes positive values greater than sbyte.MaxValue to overflow and become negative values, which may not be what you want. For example, while (sbyte)127 yields 127, (sbyte)128 yields -128. It may be that you want to translate the value range from [0, 255] to [-128, 127], in which case you can simply offset each byte by -128:

signedByte = (sbyte)(unsignedByte + sbyte.MinValue)

Upvotes: 1

Stefan Baumann
Stefan Baumann

Reputation: 46

I think that happens because of how a byte gets converted to an sbyte. Example:

sbyte b1 = 100;
sbyte b2 = -100;
Console.WriteLine("{0} = {1}", b1, (byte)b1);
Console.WriteLine("{0} = {1}", b2, (byte)b2);

This outputs the following:

100 = 100
-100 = 156

So if your wave looks the following in sbytes:

{ 0, 50, 100, 50, 0, -50, -100, -50, 0 }

The output will be the following in bytes:

{ 0, 50, 100, 50, 206, 156, 206, 0 }

Upvotes: 2

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