Summary of results¶

We compared

• decimate: the "Decimator"http://code.soundsoftware.ac.uk/projects/qm-dsp/embedded/classDecimator.html implementation in the qm-dsp library, which uses an 8-tap IIR lowpass filter;

• resample_hq, resample_mq, resample_lq: the Resampler implementation in the qm-dsp library, which uses a lengthy Kaiser-windowed sinc filter, at three different quality settings;

• src: the sndfile-resample program which uses libsamplerate, a well trusted resampler also using a Kaiser-windowed sinc implementation, at its default quality setting;

• zoh: the sndfile-resample zero-order hold resampler, which just takes every Nth sample without any filtering, serving as a baseline.

Speed¶

For 5292000 input frames on a Core i3-3229Y low-voltage CPU. (Frames-per-second values are for input frames.)

The qm-dsp implementations (resample_* and decimate) were compiled with -O3 -ffast-math while the libsamplerate implementations (src and zoh) were standard Ubuntu packages, so probably -O2. This is likely to make a very significant difference, so these results are more useful for comparison among the qm-dsp implementations than between qm-dsp and libsamplerate.

All implementations use libsndfile for audio file I/O, so that should not be a factor in overall speed.

Implementations by decimation factor¶

Factor 2¶

Frames per second	Clock time	Implementation
14225806	0.372	decimate
8939189	0.592	zoh
3732016	1.418	resample_lq
1856842	2.850	resample_mq
989158	5.350	resample_hq
516141	10.253	src

Factor 4¶

Frames per second	Clock time	Implementation
17070967	0.310	zoh
14659279	0.361	decimate
4285020	1.235	resample_lq
2186776	2.420	resample_mq
1056287	5.010	resample_hq
610099	8.674	src

Factor 8¶

Frames per second	Clock time	Implementation
26328358	0.201	zoh
13926315	0.380	decimate
4895467	1.081	resample_lq
2470588	2.142	resample_mq
1166409	4.537	resample_hq
614919	8.606	src

Factor 16¶

Frames per second	Clock time	Implementation
33493670	0.158	zoh
12721153	0.416	decimate
5093358	1.039	resample_lq
2515209	2.104	resample_mq
1182041	4.477	resample_hq
668857	7.912	src

Factor 32¶

Frames per second	Clock time	Implementation
41669291	0.127	zoh
14498630	0.365	decimate
5318592	0.995	resample_lq
2312937	2.288	resample_mq
1148936	4.606	resample_hq
670467	7.893	src

Factor 64¶

Frames per second	Clock time	Implementation
42000000	0.126	zoh
13397468	0.395	decimate
5040000	1.050	resample_lq
2365668	2.237	resample_mq
1232704	4.293	resample_hq
636057	8.320	src

Implementation zoh¶

Frames per second	Clock time	Factor
42000000	0.126	factor 64
41669291	0.127	factor 32
33493670	0.158	factor 16
26328358	0.201	factor 8
17070967	0.310	factor 4
8939189	0.592	factor 2

Implementation decimate¶

Frames per second	Clock time	Factor
14659279	0.361	factor 4
14498630	0.365	factor 32
14225806	0.372	factor 2
13926315	0.380	factor 8
13397468	0.395	factor 64
12721153	0.416	factor 16

Implementation resample_hq¶

Frames per second	Clock time	Factor
1232704	4.293	factor 64
1182041	4.477	factor 16
1166409	4.537	factor 8
1148936	4.606	factor 32
1056287	5.010	factor 4
989158	5.350	factor 2

Implementation resample_mq¶

Frames per second	Clock time	Factor
2515209	2.104	factor 16
2470588	2.142	factor 8
2365668	2.237	factor 64
2312937	2.288	factor 32
2186776	2.420	factor 4
1856842	2.850	factor 2

Implementation resample_lq¶

Frames per second	Clock time	Factor
5318592	0.995	factor 32
5093358	1.039	factor 16
5040000	1.050	factor 64
4895467	1.081	factor 8
4285020	1.235	factor 4
3732016	1.418	factor 2

Implementation src¶

Frames per second	Clock time	Factor
670467	7.893	factor 32
668857	7.912	factor 16
636057	8.320	factor 64
614919	8.606	factor 8
610099	8.674	factor 4
516141	10.253	factor 2