Re: [SoX-users] Channels/remix does not function as documented

[William M. <wm...@ke...>]

Upon examination, the main difference with your code is that when building
the effect chain, the order of adding effects you use was:

input, output, channels(remix) - which works as expected

mine was:

input, channels(remix), output - which gives 1/2 length.

Changing my code to your order works.

Was the required order documented anywhere? If so, sorry I missed it.

Thanks for looking into this!



Jan Stary wrote:
> 
>> William Mortimore wrote:
>> > In the sox man pages it says:
>> > For example, the following two commands are equivalent:
>> > sox input.wav -c 1 output.wav bass -3
>> > sox input.wav	output.wav bass -3 channels 1
>> > though the second form is more flexible as it allows the effects to be
>> > ordered arbitrarily.
>> > 
>> > Well actually they are not. With a 2 channel input file, the first way
>> > gives a mono file, but one that is 1/2 the length - it stops exactly in
>> > the middle.
>> > 
>> > The second way works properly.
>> > 
>> > Try it yourself.
> 
> Both work as expected, see 
> http://permalink.gmane.org/gmane.comp.audio.sox/3974
> 
>> > Putting the "channels" effect in the chain with or without a 1 argument
>> > results in a mono file that is 1/2 length file. 
> 
>> > In an effects chain there is no way to simulate the second way.
> 
> "Simulate"? You just add the "channels" effect to the chain.
> 
> On Dec 08 12:08:37, William Mortimore wrote:
>> Attached is a small c program that demonstrates the behavior.
>> http://old.nabble.com/file/p32937160/mixdownexample.c
> 
> I think the problem is in your application, not in libsox.
> See the code below, built around example0.c, which works
> as expected with either "channels" or "remix".
> 
> 	Jan
> 
> 
> 
> #include <stdio.h>
> #include <sox.h>
> 
> void
> usage()
> {
> 	fprintf(stderr, "usage: remix input output\n");
> }
> 
> int
> main(int argc, char** argv)
> {
> 	char *inputfile, *outputfile;
> 	sox_format_t *in, *out;
> 	sox_effects_chain_t *chain;
> 	sox_effect_t *e;
> 	char* args[10];
> 	int channels;
> 
> 	if (argc < 3) {
> 		usage();
> 		return -1;
> 	}
> 
> 	inputfile = argv[1];
> 	outputfile = argv[2];
> 
> 	sox_format_init();
> 	sox_globals.verbosity = 5;
> 
> 	in = sox_open_read(inputfile, NULL, NULL, NULL);
> 
> 	channels = in->signal.channels;
> 	in->signal.channels = 1;
> 	out = sox_open_write(outputfile, &in->signal, NULL, NULL, NULL, NULL);
> 	in->signal.channels = channels;
> 
> 	chain = sox_create_effects_chain(&in->encoding, &out->encoding);
> 
> 	e = sox_create_effect(sox_find_effect("input"));
> 	args[0] = (char*)in, sox_effect_options(e, 1, args);
> 	sox_add_effect(chain, e, &in->signal, &in->signal);
> 
> 	e = sox_create_effect(sox_find_effect("output"));
> 	args[0] = (char*)out, sox_effect_options(e, 1, args);
> 	sox_add_effect(chain, e, &in->signal, &in->signal);
> 
> 	e = sox_create_effect(sox_find_effect("channels"));
> 	args[0] = "1", sox_effect_options(e, 1, args);
> 	sox_add_effect(chain, e, &in->signal, &in->signal);
> 
> 	/*
> 	e = sox_create_effect(sox_find_effect("remix"));
> 	args[0] = "-", sox_effect_options(e, 1, args);
> 	sox_add_effect(chain, e, &in->signal, &in->signal);
> 	*/
> 
> 	sox_flow_effects(chain, NULL,NULL);
> 	sox_delete_effects_chain(chain);
> 
> 	sox_close(in);
> 	sox_close(out);
> 	sox_format_quit();
> 
> 	return 0;
> }
> 
> 
> 
> $ cc -o remix remix.c -lsox -I /usr/local/include/ -L /usr/local/lib
> $ sox -c 2 -n in.wav trim 0 10
> $ soxi in.wav
> 
> Input File     : 'in.wav'
> Channels       : 2
> Sample Rate    : 48000
> Precision      : 32-bit
> Duration       : 00:00:10.00 = 480000 samples ~ 750 CDDA sectors
> File Size      : 3.84M
> Bit Rate       : 3.07M
> Sample Encoding: 32-bit Signed Integer PCM
> 
> $ ./remix in.wav out.wav
> 
> formats: detected file format type `wav'
> wav: WAV Chunk fmt 
> wav: EXTENSIBLE
> wav: WAV Chunk fact
> wav: WAV Chunk data
> wav: Reading Wave file: Microsoft PCM format, 2 channels, 48000 samp/sec
> wav:         384000 byte/sec, 8 block align, 32 bits/samp, 3840000 data
> bytes
> wav:         480000 Samps/chans
> wav: Writing Wave file: Microsoft PCM format, 1 channel, 48000 samp/sec
> wav:         192000 byte/sec, 4 block align, 32 bits/samp
> remix: 0: 
> remix: 	0 0.5
> remix: 	1 0.5
> wav: Finished writing Wave file, 1920000 data bytes 480000 samples
> 
> (note how the "channels" effect in fact calls the "remix" effect.)
> 
> $ soxi out.wav
> 
> Input File     : 'out.wav'
> Channels       : 1
> Sample Rate    : 48000
> Precision      : 32-bit
> Duration       : 00:00:10.00 = 480000 samples ~ 750 CDDA sectors
> File Size      : 1.92M
> Bit Rate       : 1.54M
> Sample Encoding: 32-bit Signed Integer PCM
> 
> 
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