1Here are some helper programs for checking filter and rate conversion
2accuracy of sox.  The programs in the test subdirectory which I
3(Stanley J. Brooks) wrote are covered by the GPL.  See the
4../LICENSE.GPL file for details.  Sox is also covered by the GPL.
5
6To use this stuff, first cd to this test subdirectory and run make,
7which should produce the corr, model, and lmodel executables.
8
9Now to test something...
10
11Say you want to compare the 'band' effect to the 'filter' effect...
12
13./ltest.pl band 800 200 >A
14./ltest.pl filter 600-1000 >B
15gnuplot responseAB
16
17plots the response curves with y being power-gain in dB,
18and x the frequency.
19
20For another, say to compare response and error of resample
21rate conversion from 8000 ->22050 samples per second,
22with linear (default) interpolation versus -qs quadratic
23interpolation with Nuttall window...
24
25./ltest.pl -l resample >A
26./ltest.pl -l resample -qs 0.80 0 >B
27gnuplot plotAB
28
29The script wtest.pl is for testing sox's adpcm and gsm wav support.
30
31It accepts one of these options:
32    -t  Use 'toast' gsm for compress/decompress
33    -a  Use sox (MS) ADPCM
34    -i  Use sox IMA ADPCM
35    -g  Use sox wav-gsm6.10
36If using sox, you may also append an optional effect, eg:
37    ./wtest -g filter 0-3500 >A
38will apply a lowpass filter with 6dB corner at 3500 Hz before the
39compression phase.
40
41Then, as above, 'gnuplot plotA' will graph dB gain and dB error-level
42vs. freq for you.
43
44-------------------------------------------------------------------
45
46About ltest:
47
48-l means use 32-bit signed samples, otherwise 16-bit signed is used.
49
50The other parameters are fed into sox as the 'effect' with parameters.
51
52The rates 8000:22050 are in the script, but you can edit a perl script,
53I hope. just change the ($rate0,$rate1)=(8000,22050) line near the top.
54
55What ltest does:
56
57It uses sox to synthesize a sineusoid input file for the
58frequencies 0.01 ... 0.99 of the Nyquist frequency.  This input
59has:
60     400 samples samples of silence,
61    4000 samples with smooth envelope rising to volume -v0.5
62   16000 samples at -v0.5
63    4000 samples with smooth envelope falling to 0,
64     400 sample more of silence.
65
66The rising/falling envelopes are shaped like rising, falling portions
67of the (1-cos(x)) function.
68
69Then the filter or rate-change effect is applied to this i0.xx.xx file
70to give an output file.
71
72The output file is examined by the 'model' or 'lmodel' program to analyse
73response level and error level.
74
75model works as follows:
76
77step 1:  the entire sample file is read in, and the center-of-gravity of
78         the squared samples is found.  This is the time offset which should
79         correspond to the center of the filtered/resampled tone-pulse.
80
81step 2:  let N = 16000*(rate1/rate0) be the number of samples at output rate
82         which would correspond to the 16000 sample duration at max volume.
83         We focus on the samples between
84             (center - 0.3*N)    and    (center + 0.9*N)
85         where the transient effects of attack/release envelope should be
86         small.
87         We do a least-squares fit of a sinusoid at the adjusted frequency
88         to this segment of 0.6*N samples, and print out the component
89         s2max which can be explained, and also the rms level of the 'error'
90         or unexplained part.
91
92That's pretty much it... the ltest perl-script glues it together and outputs
93adjusted data which the gnuplot will like.
94
95Modify the perl and gnuplot scripts to suit your needs.
96