diff options
Diffstat (limited to 'pica-client/echocanceller.h')
| -rw-r--r-- | pica-client/echocanceller.h | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/pica-client/echocanceller.h b/pica-client/echocanceller.h index b78a2f7..e59f8d7 100644 --- a/pica-client/echocanceller.h +++ b/pica-client/echocanceller.h @@ -51,10 +51,21 @@ class EchoCanceller { public: // frameMs is the block the filter works on and must divide the audio - // handed to processNearEnd(). tailMs is how much echo delay the filter - // can model - it has to cover the sound card's output buffer plus the - // room, and costs CPU and convergence time in proportion. - EchoCanceller(int sampleRate, int frameMs = 10, int tailMs = 150); + // handed to processNearEnd(). + // + // tailMs is the longest echo delay the filter can model at all; anything + // arriving later is invisible to it and can only be dealt with + // statistically by the residual suppressor. The fixed part of that delay + // is small - the capture path plus a metre or two of flight, call it 30ms + // - so nearly all of the tail is budget for the room's reverberation. + // + // It is not free in either direction. Too short and late reflections never + // get modelled and are heard as residual echo; too long and both the + // convergence time and the steady state misadjustment grow with the tap + // count. 300ms at 16kHz is 4800 taps, which is still fewer than the 7200 + // this ran at when calls were 48kHz with a 150ms tail - so the room + // coverage doubles and the filter is still shorter than it used to be. + EchoCanceller(int sampleRate, int frameMs = 10, int tailMs = 300); ~EchoCanceller(); bool isValid() const { return m_echo != nullptr; } |