public static FilterProfile DifferentialSPL(double phon0, double phon1, double scale)
{
FilterProfile spl = new FilterProfile();
FilterProfile spl0 = Loudness.SPL(phon0);
FilterProfile spl1 = Loudness.SPL(phon1);
for (int j = 0; j < spl1.Count; j++)
{
FreqGain fg = spl1[j];
fg.Gain = scale * (spl0[j].Gain - fg.Gain);
spl.Add(fg);
}
return(spl);
}
/// <summary>
/// Create a list of dB SPL equal-loudness values for a given 'phon' loudness
/// (from zero, threshold, to 90)
/// </summary>
/// <param name="phon"></param>
/// <returns>list of {frequency Hz, dB SPL}</returns>
public static FilterProfile SPL(double phon)
{
FilterProfile lfg = new FilterProfile();
if ((phon < 0) | (phon > 120))
{
throw new ArgumentException("Phon value out of bounds!");
}
// Setup user-defined values for equation
double Ln = phon;
for (int j = 0; j < f.Length; j++)
{
// Deriving sound pressure level from loudness level (iso226 sect 4.1)
double Af = 4.47E-3 * Math.Pow(10, (0.025 * Ln) - 1.15) + Math.Pow(0.4 * Math.Pow(10, (((Tf[j] + Lu[j]) / 10) - 9)), af[j]);
double Lp = ((10 / af[j]) * Math.Log10(Af)) - Lu[j] + 94;
// Return user data
FreqGain fg = new FreqGain(f[j], Lp);
lfg.Add(fg);
}
return(lfg);
}