TONE-MASKING NOISE

• Frequency masking: one sound cannot be perceived if another sound close in frequency has a high enough level. The first sound masks the second.
  
  
• Tone-masking noise: noise with energy E_N (dB) at Bark frequency g masks a tone at Bark frequency b if the tone's energy is below the threshold:
  
  
  T_T(b) = E_N - 6.025 - 0.275g + S_m(b-g)   (dB SPL)
  
  where the spread-of-masking function S_m(b) is given by:
  
  
  S_m(b) = 15.81 + 7.5(b+0.474)-17.5*sqrt(1 + (b+0.474)²)   (dB)
  
  
• Temporal Masking: onsets of sounds are masked in the time domain through a similar masking process.

Key points:

• Thresholds are frequency and energy dependent.
  
  
• Thresholds depend on the nature of the sound as well.