<div class="gmail_quote"><br></div><div class="gmail_quote">2011/4/20 Li Maoquan <span dir="ltr">&lt;<a href="mailto:limaoquan2000@126.com">limaoquan2000@126.com</a>&gt;</span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div class="im">Simply to say, in a quiet room, you can play a impulse signal and then find it&#39;s impulse response signal from the <br>microphone. For example, if the delay between the impulse signal and its response signal range from 500 to<br>
3000 cycles, you can buffer the far-end signal to 0-300 cycles and set the filter length to 4000. It is also called<br>to align far-end signal and near-end signal.<br><br>BTW: Speex AEC is sensiive to mismatch between sample rates of capturing and rendering. But most low-cost<br>
computer soundcards have this problem.<div></div><br></div></blockquote><div><br></div><div>Based on your explanation above, I have attempted to measure the delay between the near-end and far-end signal. I send in a sharp impulse sound, have it play on the speaker and see when it comes out of the mic. I am looking at peak amplitudes in each frame (160 samples) to identify the impulse sound.</div>
<div><br></div><div>The time from when the sound enters the stack (before it is queued with the speaker) to the time when it comes out of the mic ready to go out, varies between 0.44 to 0.57 seconds. So I queue the far-end samples for 0.4 seconds, and then send them to speex_echo_playback. Also, I am using a filter length of 0.2 seconds (1600 samples). Each outgoing (near-end) sample coming from the mic is passed through speex_echo_capture to cancel the echo and the output is sent out of the device.</div>
<div><br></div><div>Despite this, the cancellation does not seem to work. I have also tried using speex_echo_cancellation. That doesn&#39;t help either.</div><div><br></div><div>What could I be doing wrong? Any suggestions?</div>
<div>Also, I am not using the speex encoder/decoder, just the echo cancellation. I hope that&#39;s not an issue. Please correct me if it is.</div><div><br></div><div>Thanks for helping me with this!</div><div><br></div><div>
<br></div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div class="im"></div><pre><br>At&nbsp;2011-04-21&nbsp;03:00:01，<a href="mailto:speex-dev-request@xiph.org" target="_blank">speex-dev-request@xiph.org</a>&nbsp;wrote:
&gt;&gt;&nbsp;&gt;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;I&nbsp;have&nbsp;a&nbsp;scenario&nbsp;in&nbsp;a&nbsp;mobile&nbsp;VoIP&nbsp;app&nbsp;that&nbsp;requires&nbsp;echo&nbsp;cancellation
&gt;&gt;&nbsp;but
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;is&nbsp;somewhat&nbsp;different&nbsp;from&nbsp;what&#39;s&nbsp;described&nbsp;in&nbsp;the&nbsp;docs.
&gt;&gt;&nbsp;&gt;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;Audio&nbsp;is&nbsp;received&nbsp;from&nbsp;and&nbsp;sent&nbsp;to&nbsp;the&nbsp;network&nbsp;at&nbsp;8000Hz.&nbsp;Each&nbsp;packet
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;contains&nbsp;160&nbsp;samples&nbsp;worth&nbsp;a&nbsp;playback&nbsp;of&nbsp;20ms.
&gt;&gt;&nbsp;&gt;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;But&nbsp;the&nbsp;hardware&nbsp;requires&nbsp;aggregation&nbsp;for&nbsp;both&nbsp;playback&nbsp;and&nbsp;capture.&nbsp;So
&gt;&gt;&nbsp;for
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;playback,&nbsp;I&nbsp;coalesce&nbsp;4&nbsp;packets&nbsp;in&nbsp;a&nbsp;buffer&nbsp;and&nbsp;queue&nbsp;them&nbsp;as&nbsp;a&nbsp;larger
&gt;&gt;&nbsp;buffer
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;for&nbsp;playback.
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;On&nbsp;the&nbsp;send&nbsp;side,&nbsp;I&nbsp;read&nbsp;a&nbsp;large&nbsp;buffer&nbsp;(worth&nbsp;4&nbsp;packets)&nbsp;and&nbsp;send&nbsp;them
&gt;&gt;&nbsp;out
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;over&nbsp;time&nbsp;20ms&nbsp;apart.
&gt;&gt;&nbsp;&gt;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;I&nbsp;tried&nbsp;using&nbsp;speex_echo_playback&nbsp;just&nbsp;when&nbsp;a&nbsp;160-sample&nbsp;packet&nbsp;arrives
&gt;&gt;&nbsp;from
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;the&nbsp;network,&nbsp;before&nbsp;coalescing&nbsp;and&nbsp;speex_echo_capture&nbsp;just&nbsp;before&nbsp;a
&gt;&gt;&nbsp;packet
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;is&nbsp;sent&nbsp;out&nbsp;to&nbsp;the&nbsp;network&nbsp;but&nbsp;that&nbsp;doesn&#39;t&nbsp;seem&nbsp;to&nbsp;work&nbsp;properly
&gt;&gt;&nbsp;(doesn&#39;t
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;cancel&nbsp;any&nbsp;echo).
&gt;&gt;&nbsp;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&nbsp;The&nbsp;most&nbsp;likely&nbsp;reason&nbsp;is&nbsp;that&nbsp;you&nbsp;didn&#39;t&nbsp;align&nbsp;the&nbsp;far-end&nbsp;and&nbsp;near-end
&gt;&gt;&nbsp;samples.
&gt;&gt;&nbsp;&gt;&gt;&nbsp;So&nbsp;the&nbsp;filter&nbsp;can&nbsp;not&nbsp;converge.
&gt;&gt;&nbsp;&gt;
&gt;&gt;&nbsp;&gt;Thanks&nbsp;for&nbsp;your&nbsp;response.&nbsp;Can&nbsp;you&nbsp;please&nbsp;explain&nbsp;what&nbsp;you&nbsp;mean&nbsp;by
&gt;&gt;&nbsp;&gt;align&nbsp;samples&nbsp;from&nbsp;near-end&nbsp;and&nbsp;far-end?&nbsp;And&nbsp;how&nbsp;is&nbsp;that&nbsp;usually
&gt;&gt;&nbsp;&gt;accomplished?
&gt;&gt;
&gt;&gt;&nbsp;You&nbsp;need&nbsp;to&nbsp;know&nbsp;the&nbsp;total&nbsp;delay&nbsp;caused&nbsp;by&nbsp;DAC&nbsp;buffer&nbsp;before&nbsp;speaker,&nbsp;ADC
&gt;&gt;&nbsp;buffer
&gt;&gt;&nbsp;after&nbsp;microphone&nbsp;and&nbsp;acoustic&nbsp;path&nbsp;between&nbsp;speaker&nbsp;and&nbsp;microphone.&nbsp;Simply
&gt;&gt;&nbsp;to&nbsp;say,
&gt;&gt;&nbsp;if&nbsp;you&nbsp;play&nbsp;an&nbsp;impluse&nbsp;signal&nbsp;and&nbsp;its&nbsp;first&nbsp;echo&nbsp;appears&nbsp;after&nbsp;N&nbsp;sample
&gt;&gt;&nbsp;cycles,
&gt;&gt;&nbsp;you&nbsp;can&nbsp;call&nbsp;N&nbsp;as&nbsp;the&nbsp;delay&nbsp;between&nbsp;y&nbsp;(echo&nbsp;in&nbsp;near-end&nbsp;signal)&nbsp;and&nbsp;x
&gt;&gt;&nbsp;(far-end
&gt;&gt;&nbsp;signal).&nbsp;Then&nbsp;you&nbsp;can&nbsp;buffer&nbsp;far-end&nbsp;signal&nbsp;for&nbsp;N-M&nbsp;cycles&nbsp;before&nbsp;sending
&gt;&gt;&nbsp;to&nbsp;AEC.
&gt;&gt;&nbsp;M&nbsp;is&nbsp;a&nbsp;little&nbsp;number&nbsp;(such&nbsp;as&nbsp;100)&nbsp;in&nbsp;order&nbsp;to&nbsp;avoid&nbsp;filter&nbsp;failure&nbsp;when
&gt;&gt;&nbsp;echo
&gt;&gt;&nbsp;path&nbsp;drifts.
&gt;&gt;
&gt;&gt;
&gt;Thanks&nbsp;again.&nbsp;I&nbsp;am&nbsp;trying&nbsp;to&nbsp;model&nbsp;the&nbsp;delay&nbsp;between&nbsp;the&nbsp;near&nbsp;and&nbsp;far&nbsp;end
&gt;signals&nbsp;using&nbsp;a&nbsp;circular&nbsp;queue&nbsp;of&nbsp;length&nbsp;n.&nbsp;Every&nbsp;time&nbsp;a&nbsp;frame&nbsp;is&nbsp;received
&gt;and&nbsp;queued&nbsp;for&nbsp;playback,&nbsp;it&nbsp;is&nbsp;also&nbsp;entered&nbsp;into&nbsp;the&nbsp;queue.&nbsp;Each&nbsp;frame&nbsp;being
&gt;read&nbsp;from&nbsp;the&nbsp;mic&nbsp;is&nbsp;echo-cancelled&nbsp;(&nbsp;speex_echo_cancellation&nbsp;)&nbsp;using&nbsp;the
&gt;oldest&nbsp;frame&nbsp;in&nbsp;the&nbsp;queue&nbsp;if&nbsp;the&nbsp;queue&nbsp;is&nbsp;filled&nbsp;up,&nbsp;thus&nbsp;I&nbsp;am&nbsp;cancelling
&gt;the&nbsp;recorded&nbsp;frame&nbsp;using&nbsp;a&nbsp;playback&nbsp;frame&nbsp;that&nbsp;is&nbsp;N-frames&nbsp;old.
&gt;
&gt;I&nbsp;have&nbsp;played&nbsp;with&nbsp;different&nbsp;values&nbsp;of&nbsp;N&nbsp;from&nbsp;2&nbsp;to&nbsp;50&nbsp;(320&nbsp;samples&nbsp;to&nbsp;8000
&gt;samples),&nbsp;attempting&nbsp;to&nbsp;align&nbsp;the&nbsp;input&nbsp;and&nbsp;output&nbsp;but&nbsp;the&nbsp;cancellation
&gt;doesn&#39;t&nbsp;seem&nbsp;to&nbsp;work.&nbsp;The&nbsp;echo&nbsp;is&nbsp;steady&nbsp;as&nbsp;ever.
&gt;
&gt;Is&nbsp;this&nbsp;model&nbsp;correct&nbsp;and&nbsp;expected&nbsp;to&nbsp;converge&nbsp;with&nbsp;a&nbsp;right&nbsp;value&nbsp;of&nbsp;&quot;N&quot;?&nbsp;Or
&gt;do&nbsp;I&nbsp;need&nbsp;some&nbsp;other&nbsp;adaptation&nbsp;to&nbsp;account&nbsp;for&nbsp;drifts&nbsp;here.&nbsp;Right&nbsp;now,&nbsp;it&#39;s
&gt;a&nbsp;black&nbsp;box&nbsp;for&nbsp;me.&nbsp;I&nbsp;am&nbsp;not&nbsp;sure&nbsp;how&nbsp;to&nbsp;get&nbsp;some&nbsp;feedback&nbsp;from&nbsp;this&nbsp;system
&gt;to&nbsp;tune&nbsp;the&nbsp;AEC&nbsp;(and&nbsp;the&nbsp;delay&nbsp;parameters)&nbsp;correctly.
&gt;
&gt;Also,&nbsp;I&nbsp;did&nbsp;not&nbsp;follow&nbsp;the&nbsp;use&nbsp;of&nbsp;&quot;M&quot;&nbsp;in&nbsp;your&nbsp;description&nbsp;above&nbsp;and&nbsp;how&nbsp;it
&gt;helps&nbsp;with&nbsp;drifts.&nbsp;My&nbsp;queue&nbsp;stores&nbsp;frames&nbsp;(160&nbsp;samples&nbsp;each).&nbsp;So&nbsp;a&nbsp;number&nbsp;of
&gt;100&nbsp;samples&nbsp;seems&nbsp;too&nbsp;small.
&gt;
&gt;Btw,&nbsp;I&nbsp;am&nbsp;assuming&nbsp;that&nbsp;speex&nbsp;AEC&nbsp;API&nbsp;can&nbsp;be&nbsp;used&nbsp;even&nbsp;though&nbsp;I&nbsp;am&nbsp;not&nbsp;using
&gt;the&nbsp;speex&nbsp;encoder/decoder.
&gt;
&gt;
&gt;
&gt;&gt;&nbsp;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;&gt;&nbsp;So,&nbsp;in&nbsp;this&nbsp;scenario&nbsp;above,&nbsp;please&nbsp;recommend&nbsp;a&nbsp;good&nbsp;place&nbsp;to&nbsp;insert
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;speex_echo_playback&nbsp;and&nbsp;speex_echo_capture.&nbsp;Should&nbsp;I&nbsp;be&nbsp;just&nbsp;before&nbsp;the
&gt;&gt;&nbsp;read
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;and&nbsp;write&nbsp;to&nbsp;hardware?&nbsp;In&nbsp;that&nbsp;case,&nbsp;should&nbsp;I&nbsp;use&nbsp;a&nbsp;larger&nbsp;&quot;frame&nbsp;size&quot;
&gt;&gt;&nbsp;of
&gt;&gt;&nbsp;&gt;&gt;&gt;&nbsp;160&nbsp;samples&nbsp;x&nbsp;4?
&gt;&gt;&nbsp;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&nbsp;Of&nbsp;course&nbsp;you&nbsp;can&nbsp;set&nbsp;frame&nbsp;size&nbsp;to&nbsp;160*4.&nbsp;Otherwise&nbsp;you&nbsp;can&nbsp;feed
&gt;&gt;&nbsp;samples&nbsp;4&nbsp;times
&gt;&gt;&nbsp;&gt;&gt;&nbsp;to&nbsp;the&nbsp;AEC&nbsp;if&nbsp;you&nbsp;don&#39;t&nbsp;want&nbsp;to&nbsp;modify&nbsp;the&nbsp;frame&nbsp;size.
&gt;&gt;&nbsp;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&gt;
&gt;&gt;&nbsp;&gt;&gt;&nbsp;Thanks&nbsp;in&nbsp;advance,
&gt;&gt;&nbsp;&gt;&gt;&nbsp;Daniel.

</pre><pre></pre><br><br><span title="neteasefooter"><span><hr>
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