Increase volume by X decibels and rewrite audio file

Question

I'm new in naudio. And I wanna increase volume by X db. I've written this piece of code:

public static void IncreaseVolume(string inputPath, string outputPath, double db)
{            
    double linearScalingRatio = Math.Pow(10d, db / 10d);
    using (WaveFileReader reader = new WaveFileReader(inputPath))
    {
        VolumeWaveProvider16 volumeProvider = new VolumeWaveProvider16(reader);
        using (WaveFileWriter writer = new WaveFileWriter(outputPath, reader.WaveFormat))
        {
            while (true)
            {
                var frame = reader.ReadNextSampleFrame();
                if (frame == null)
                    break;
                writer.WriteSample(frame[0] * (float)linearScalingRatio);
            }
        }
    }
}

Ok, this works, but how can I find by how many decibels I've increased each sample? May anyone explain this moment for me and provide any examples?

UPDATE:

 using (WaveFileReader reader = new WaveFileReader(inFile))
            {
                float Sum = 0f;
                for (int i = 0; i < reader.SampleCount; i++)
                {
                    var sample = reader.ReadNextSampleFrame();
                    Sum += sample[0] * sample[0];
                }
                var db =  20 * Math.Log10(Math.Sqrt(Sum / reader.SampleCount) / 1);               
                Console.WriteLine(db);
                Console.ReadLine();
            }

Answer 1

Your code looks good. To measure the average sound level of an audio sample you need to calculate the RMS (root mean square) of this sound level:

RMS := Sqrt( Sum(x_i*x_i)/N)

with x_i being the i-th sample and N the number of samples. The RMS is the average amplitude of your signal. Use

RMS_dB = 20*log(RMS/ref)

(with ref being 1.0 or 32767.0)

to convert it to a decibel value.

You may calculate this RMS value before and after you change the volume. The difference should be erxactly the dB you used in your IncreaseVolume()