1) Masking occurs when a louder sound (the masker) makes a softer sound (the maskee) inaudible. There are two types of masking - simultaneous (frequency) masking which occurs when sounds are at the same time/frequency, and temporal (non-simultaneous) masking which occurs when sounds are not simultaneous. 2) Masking curves are used to measure masking and different curves result from different combinations of masker and maskee types (e.g. noise masking tone, tone masking tone, noise/tone masking noise). Models have also been developed to describe the spreading of masking across frequencies. 3) In summary, the document discussed masking and its types, definitions,