ios - Auto-correlating the cepstrum -


i'm trying detect echoes in sound coming microphone. echoes periodic , @ 1 of 2 possible offsets. i've heard need auto-correlate cepstrum of signal in order detect presence of these echoes. can provide code using accelerate framework shows how detect echoes in audio data?

i'm not entirely sure why you'd auto correlate cepstrum. auto correlation, though, gives representation related cepstrum assume want auto correlate signal.

in simplest form performed follows:

int sample      = 0; int samplemax   = insize;  while( sample < samplemax ) {             vdsp_vsmul( pinput, 1, pinputsample, tempbuffer, 1, samplemax );      const size_t kautocorrwritepos  = outsize - samplemax - sample;             vdsp_vsadd( &poutput[kautocorrwritepos], 1, tempbuffer, 1, &poutput[kautocorrwritepos], 1, samplemax )     sample++; }

this is, however, slow operation. thankfully correlation can performed in several different ways. fastest method perform fft, multiply complex values conjugate of , inverse fft.

or in ios have nicely optimised vdsp_conv function:

std::vector< float > paddedbuffer( (insize + insize) - 1 ); memcpy( &paddedbuffer.front(), pinput, sizeof( float ) * insize ); vdsp_conv( &paddedbuffer.front(), 1, (float*)pinput, 1, (float*)poutput + (insize - 1), 1, insize, insize );  // reflect auto correlation true output. int poswrite    = (insize - 1); int posread     = (insize - 1); while( poswrite > 0 ) {     poswrite--;     posread++;      poutput[poswrite] = poutput[posread]; }

so have auto correlation, d o it?

well firstly right in middle have highest peak. 0 lag point. want scan right of central peak identify secondary peaks. if yo looking specific peak @ specific offset can, simply, check number of samples on central peak , check if there peak there. if there isn't signal looking not there. if there, signal there.

edit: worth noting 512 sample wide window if lag looking @ beyond 128 may not enough of correlation signal spottable. correlation works providing peaks @ points of repetitive signals in sample data. @ lag of 128 have enough data point repeat 4 times. @ 256 can see point repeat twice. affect height of correlation peak. after 256 may not spot peak @ against random repeatability factors. said, though, experiment different window sizes see provides reliable results.


Comments

Post a Comment

Popular posts from this blog

php - cannot display multiple markers in google maps v3 from traceroute result -

i'm newbie in php mysql , google maps v3. have problems in google maps v3. made traceroute web based , map traceroute's result in google maps v3 final project of college education. have try many tutorials didn't work. have tried tutorials in forum nothing worked. problem cannot display multiple markers got location data database. maybe because i'm newbie , not know how do. confuse looping show markers. here code <?php error_reporting(e_all ^ (e_notice)); ini_set('max_execution_time', 360); $enable_log_user = false; global $ip, $host_name, $host_ip; $host = @$_post['host']; $trace = @$_post['trace']; $self = $_server['php_self']; include("phpsqlajax_dbinfo.php"); $connection = mysql_connect ('127.0.0.1', $username, $password); if (!$connection) { die('not connected : ' . mysql_error());} $db_selected = mysql_select_db($database, $connection); if (!$db_selected) { die ('can\'t use db :
Read more

c# - DetailsView in ASP.Net - How to add another column on the side/add a control in each row? -

i have detailsview control on page used edit various fields of record, works in respect. i looking way add 1 column (and if works, why not more) right, absolutely read-only, show same fields of record comparison purposes. i aware there no obvious way such thing out of box detailsview . have looked other controls (transposed gridview , recommended formview , listview ), nothing satisfies. have special data binding setup using detailsview , can't out of without losing features. anyone on how "hack in" additional columns (for display only) on detailsview ? the solution have now, use second detailsview , visible set false in aspx. in code, make sure databind hidden detailsview hosts data third column first, initial detailsview named itemdetails . and in item created event, pass third column html rendering of hidden controls (in last code block) : protected void itemdetails_itemcreated(object sender, eventargs e) { if (dataite
Read more

javascript - firefox memory leak -

i have following script (i use raphaeljs also) draws circle, waits 1 second, draws circle again, etc (you can copy paste - functional, need include raphael raphaeljs.com): <div id="holder"> </div> <script src="raphael.js" type="text/javascript"></script> <script> var paper = raphael(10, 50, 320, 200); var rad = math.pi / 180; var finangle = 0; function sector(cx, cy, r, startangle, endangle, params) { var x1 = cx + r * math.cos(-startangle * rad), x2 = cx + r * math.cos(-endangle * rad), y1 = cy + r * math.sin(-startangle * rad), y2 = cy + r * math.sin(-endangle * rad); return ["m", cx, cy, "l", x1, y1, "a", r, r, 0, +(endangle - startangle > 180), 0, x2, y2]; } var path = sector(100,100,50,0,180); var arc = paper.path(path); function draw() { path = sector(100,100,50,0,finangle);
Read more