I  had a bit of a lull!   But I did reach  an end-point  to convolving
wavs. I'm going to post three non-portable ecl packages 

warm

WAv transfoRM- exports using libsndfile
(warm:transform "song-in.wav" "song-out.wav"
(lambda (list) (mapcar (lambda  (X) (* 0.5d0 x)) list))
 (lambda (list) #'nreverse))
Strides    through   song-in   in  4096  length  chunks  as  lists  of
double-floats writing to song-out.  Where the two strings are paths of
wav to read and wav to write, and the two lambdas  happen  to the left
and right channels respectively. The wav is two channel, and pcm_f64le
as from 

ffmpeg -i my-fave.mp3 -c:a pcm_f64le song-in.wav

I  actually   wrote  warm  for  last  week's   show  (those   terrible
transforms),  but I was unhappy with it, since I wanted  it to just be
example/sf_process/   from libsndfile  and it wound up a bit different
and made of spaghetti. 

cold

exports using fftw
(cold:fftw-convolve)
Which r2c .. c2r transforms  two length 4096 double arrays to convolve
them.   Since those two arrays are statically  allocated   (what  does
static mean), it has ugly accessor functions  for filling them.  tepid
is an example usage. 

tepid

kloogetacular utility that does this, completely improperly:

./tepid -i song-in.wav -o song-out.wav -f 321 > chunk-maxes.txt

song-out  is totally  useless, because it's not scaled  down to proper
-1..1 f64le values. It would be too loud to play, by a lot. However as
a side effect  it outputs the maximum of the matched  filter  response

**Patch: Now just transforms the left channel to a listenable frequency
**      response (of the right channel). Awesome.

(convolution) for each chunk, suitably for gnuploting like 

gnuplot -p -e "plot 'chunk-maxes.txt' with lines;

For which  if my frequency  math is actually right,  the peaks  are of
that  frequency.   Definitely  different  frequencies   get  different
responses. 

I'll upload  them before  my show,  which  I will do completely   live
today.  I'm not a good enough DJ to be rocking person handcrafted  mix
tapes (yet). I'll patch them a little to be saner. 

I  hope we can keep rolling  with our incipient  lisp group.   I asked
ldbeth   who  has  recently  upgraded  his phlog  and  listed   it  on
gopher.club    to  pick  a  next  topic,   which  will  be   something
electronicsy.