Acoustic echo cancellation
in [DSP]
|
From: createdon2003 on 2 Sep 2009 07:46 Hi all, I am working on acoustic echo canceler for mobile telephony. I have two doubts to clarify: 1) Avi perry in his book "Voice Quality Engineering in Wireless Networks" has mentioned that although speech signal power is distributed almost uniformly across the entire spectrum, the acoustic echo power concentrates most of its energy in the 1700-2500 Hz range. Anybody having any idea of the possible explanation. 2) I am searching a bulk delay estimation method (for AEC)that can be used in the presence of heavy non-linear distortions. These non linear distortions are introduced by : GSM codec, Speaker, Mechanical/Acoustic coupling. I will be very thankful if anyone can guide me through. Any good books that deal with Acoustic Echo Cancelers in wireless network. Thanks Sankalp
From: Vladimir Vassilevsky on 2 Sep 2009 10:06 createdon2003 wrote: > Hi all, > > I am working on acoustic echo canceler for mobile telephony. I have two > doubts to clarify: > > 1) Avi perry in his book "Voice Quality Engineering in Wireless Networks" > has mentioned that although speech signal power is distributed almost > uniformly across the entire spectrum, ???? Average speech signal power has maximum at few hundred Hz and then rolls down towards the high frequencies with the rate about 10dB/oct. > the acoustic echo power concentrates > most of its energy in the 1700-2500 Hz range. Anybody having any idea of > the possible explanation. A misprint, perhaps. More likely, they meant 170...2500. > 2) I am searching a bulk delay estimation method (for AEC)that can be used > in the presence of heavy non-linear distortions. Run a traditional *.LMS algorithm over all span of the expected delay. Then look at the resulting impulse response; the bulk delay part will be seen clearly. To keep the computations reasonable, you can decimate the signal to the lower sampling rate. > These non linear > distortions are introduced by : GSM codec, Speaker, Mechanical/Acoustic > coupling. I will be very thankful if anyone can guide me through. Auch. I doubt you can achieve any good result if you have a vocoder in the EC loop. The compensation of the small nonlinearities is feasible; it is better done in the frequency domain EC. However I don't know of any practical EC system which employs the nonlinear compensation. > Any good books that deal with Acoustic Echo Cancelers in wireless > network. The EC loop is closed at the ends of the link; it doesn't matter what kind of network is in between. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: createdon2003 on 2 Sep 2009 10:46 thanks for the reply... > > >createdon2003 wrote: >> Hi all, >> >> I am working on acoustic echo canceler for mobile telephony. I have two >> doubts to clarify: >> >> 1) Avi perry in his book "Voice Quality Engineering in Wireless Networks" >> has mentioned that although speech signal power is distributed almost >> uniformly across the entire spectrum, > >???? > >Average speech signal power has maximum at few hundred Hz and then rolls >down towards the high frequencies with the rate about 10dB/oct. > >> the acoustic echo power concentrates >> most of its energy in the 1700-2500 Hz range. Anybody having any idea of >> the possible explanation. > >A misprint, perhaps. More likely, they meant 170...2500. Actually I have verified it through a real recording, but couln't find the reason. I am suspecting the mechanical coupling because of the poor casing..ne idea???..how does that coupling is modeled (Frequency response n all)..couln't find it anywhere.. > >> 2) I am searching a bulk delay estimation method (for AEC)that can be used >> in the presence of heavy non-linear distortions. > >Run a traditional *.LMS algorithm over all span of the expected delay. >Then look at the resulting impulse response; the bulk delay part will be >seen clearly. To keep the computations reasonable, you can decimate the >signal to the lower sampling rate. > >> These non linear >> distortions are introduced by : GSM codec, Speaker, Mechanical/Acoustic >> coupling. I will be very thankful if anyone can guide me through. > >Auch. I doubt you can achieve any good result if you have a vocoder in >the EC loop. >The compensation of the small nonlinearities is feasible; it is better >done in the frequency domain EC. However I don't know of any practical >EC system which employs the nonlinear compensation. > >> Any good books that deal with Acoustic Echo Cancelers in wireless >> network. > >The EC loop is closed at the ends of the link; it doesn't matter what >kind of network is in between. Sorry probably it wasn't very clearly written. I meant GSM network (Vocoders are present in both directions). > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com > > > Sankalp
From: Vladimir Vassilevsky on 2 Sep 2009 11:01 createdon2003 wrote: > Sorry probably it wasn't very clearly written. I meant GSM network > (Vocoders are present in both directions). If you have vocoders in the loop, the EC is not feasible. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: createdon2003 on 3 Sep 2009 01:28 >> the acoustic echo power concentrates >> most of its energy in the 1700-2500 Hz range. Anybody having any idea of >> the possible explanation. > >A misprint, perhaps. More likely, they meant 170...2500. Actually I have verified it through a recording (not sure whether speaker phone was on/off)that acoustic echo's power was present mainly between 1700-2500Hz, but couln't find the reason. I am suspecting the poor acoustic isolation due to cheap casing..any idea???..how does that coupling is modeled (Frequency response n all)..couln't find it anywhere.. Sankalp
|
Next
|
Last
Pages: 1 2 3 4 Prev: PPI Interface Clock in BF537 EZLITE Board Next: Sliding Block Viterbi Decoder |