Controlling ambient sound volume
An earpiece includes a feed-forward microphone coupled to the environment outside the headphones, a feedback microphone coupled to an ear canal of a user when the earpiece is in use, a speaker coupled to the ear canal of the user when the earpiece is in use, a digital signal processor implementing feed-forward and feedback noise compensation filters between the respective microphones and the speaker, and a memory storing an ordered sequence of sets of filters for use by the digital signal processor. Each of the sets of filters includes a feed-forward filter that provides a different frequency-dependent amount of sound pass-through or cancellation, which in combination with residual ambient sound reaching the ear results in a total insertion gain at the ear of a user.
1. An apparatus comprising:
an earpiece having a feed-forward microphone coupled to the environment outside the earpiece, a speaker coupled to the ear canal of the user when the earpiece is in use, a digital signal processor implementing feed-forward noise compensation filters between the feed-foward microphone and the speaker, and a memory storing an ordered sequence of sets of filters for use by the digital signal processor; wherein
each of the sets of filters includes a feed-forward filter that provides a different frequency-dependent amount of sound pass-through or cancellation, which in combination with residual ambient sound reaching the ear results in a total insertion gain at the ear of a user,
at least a subset of the sets of filters further providing the same response over at least 3 octaves in the human voice band, and adding ambient sound at different levels outside of the human voice band when compared to the insertion gain achieved in a full active noise reduction (ANR) mode.
2. The apparatus of claim 1 , wherein the change in overall sound level at the ear when switching between adjacent filters in the sequence is substantially constant over the whole sequence of filters.
3. The apparatus of claim 1 , wherein the change in overall sound level at the ear when switching between adjacent filters in the sequence is a substantially smooth function over the whole sequence of filters.
4. The apparatus of claim 3 , wherein the function progresses from a smaller amount of change between filters providing less total noise reduction to a larger amount of change between filters providing more total noise reduction.
5. The apparatus of claim 1 , wherein the overall sound level at the ear when using each of the sets of filters, for a given ambient sound level, differs from the overall sound level at the ear when using the adjacent set of filters in the sequence by an amount that is not perceptible to a typical human.
6. The apparatus of claim 1 , wherein the overall sound level at the ear when using each of the sets of filters, for a given ambient sound level, differs from the overall sound level at the ear when using the adjacent set of filters in the sequence by no more than 3 dBA for a majority of changes between any two adjacent filter sets in the sequence.
7. The apparatus of claim 6 , wherein the overall sound level at the ear when using each of the sets of filters, for a given ambient sound level, differs from the overall sound level at the ear when using the adjacent set of filters in the sequence by no more than 1 dBA for a majority of changes between any two adjacent filter sets in the sequence.
8. The apparatus of claim 1 , wherein the change in overall sound level at the ear when switching between adjacent filters in the sequence is a substantially smooth function over the whole sequence of filters.
9. The apparatus of claim 8 , wherein the function progresses from a smaller amount of change between filters providing less total noise reduction to a larger amount of change between filters providing more total noise reduction.