5.4-- Sample rate conversion

The sample rates currently supported are as follows:

The converters are implemented using "hard-wired" FIR filters to provide the low-pass anti-aliasing (for downsampling) and anti-imaging (for upsampling) protection. The filters for all converters have been designed according to the following specification:

Design specifications for FIR filters used in all sample-rate converters
Lowpass edge frequency	Nyquist rate associated with given conversion: i.e. half the output sample-rate for downsampling, and half the input sample-rate for upsampling.
stopband attenuation	>=120 dB
passband attenuation	<=0.01 dB

Moreover, for computational efficiency, the filters are implemented in multi-stage polyphase form, whereby a given conversion ratio is achieved via a cascade of converters, within each of which the filtering is always carried out at the lower sample rate. The composite (overall) effect of the multiple stages achieves the desired conversion ratio according to the overall lowpass specification in the previous table. The detailed breakdown of the multi-stage design for each converter is summarized as follows:

Input (Hz)	Output (Hz)	Multi-stage conversion factors	FIR filter lengths (per stage)
8000	11025	(2/1)*(3/1)*(3/1)*(7/1)*(7/640)=882/640	475, 33, 19, 43, 41
8000	16000	2/1	431
8000	22050	(2/1)*(3/1)*(3/1)*(7/1)*(7/320)=882/320	475, 33, 19, 43, 41
8000	32000	(2/1)*(2/1)=4/1	449, 19
8000	44100	(2/1)*(3/1)*(3/1)*(7/1)*(7/160)=882/160	475, 33, 19, 43, 41
8000	48000	(2/1)*(3/1)=6/1	449, 31
8000	96000	(2/1)*(6/1)=12/1	449, 65
8000	192000	(2/1)*(3/1)*(4/1)=24/1	461, 33, 25
11025	8000	(640/7)*(1/7)*(1/3)*(1/3)*(1/2)=640/882	41, 43, 19, 33, 475
11025	16000	(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/441)=640/441	479, 21, 13, 9, 31, 47
11025	22050	2/1	431
11025	32000	(2/1)*(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/441) =1280/441	483, 21, 13, 9, 9, 29, 47
11025	44100	(2/1)*(2/1)=4/1	449, 19
11025	48000	(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147)=640/147	479, 21, 13, 9, 31, 47
11025	96000	(2/1)*(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147) =1280/147	483, 21, 13, 9, 9, 29, 47
11025	192000	(2/1)*(2/1)*(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147) =2560/147	487, 21, 13, 9, 9, 7, 29, 49
16000	8000	½	431
16000	11025	(441/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)=441/640	47, 31, 9, 13, 21, 479
16000	22050	(2/1)*(3/1)*(3/1)*(7/1)*(7/640)=882/640	475, 33, 19, 43, 41
16000	32000	2/1	431
16000	44100	(2/1)*(3/1)*(3/1)*(7/1)*(7/320)=882/320	475, 33, 19, 43, 41
16000	48000	(2/1)*(3/2)=6/2	449, 31
16000	96000	(2/1)*(3/1)=6/1	449, 31
16000	192000	(2/1)*(6/1)=12/1	449, 65
22050	8000	(320/7)*(1/7)*(1/3)*(1/3)*(1/2)=320/882	41, 43, 19, 33, 475
22050	11025	½	431
22050	16000	(640/7)*(1/7)*(1/3)*(1/3)*(1/2)=640/882	41, 43, 19, 33, 475
22050	32000	(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/441)=640/441	479, 21, 13, 9, 31, 47
22050	44100	2/1	431
22050	48000	(2/1)*(2/1)*(2/1)*(5/1)*(8/147)=320/147	475, 21, 13, 33, 49
22050	96000	(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147)=640/147	479, 21, 13, 9, 31, 47
22050	192000	(2/1)*(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147) =1280/147	483, 21, 13, 9, 9, 29, 47
32000	8000	(1/2)*(1/2)=1/4	19, 449
32000	11025	(441/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2) =441/1280	47, 29, 9, 9, 13, 21, 483
32000	16000	½	431
32000	22050	(441/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)=441/640	47, 31, 9, 13, 21, 479
32000	44100	(2/1)*(3/1)*(3/1)*(7/1)*(7/640)=882/640	475, 33 , 19, 43, 41
32000	48000	(2/1)*(3/4)=6/4	449, 31
32000	96000	(2/1)*(3/2)=6/2	449, 31
32000	192000	(2/1)*(3/1)=6/1	449, 31
44100	8000	(160/7)*(1/7)*(1/3)*(1/3)*(1/2)=160/882	41, 43, 19, 33, 475
44100	11025	(1/2)*(1/2)=1/4	19, 449
44100	16000	(320/7)*(1/7)*(1/3)*(1/3)*(1/2)=320/882	41, 43, 19, 33, 475
44100	22050	½	431
44100	32000	(640/7)*(1/7)*(1/3)*(1/3)*(1/2)=640/882	41, 43, 19, 33, 475
44100	48000	(2/1)*(2/1)*(5/1)*(8/147)=160/147	469, 21, 37, 49
44100	96000	(2/1)*(2/1)*(2/1)*(5/1)*(8/147)=320/147	475, 21, 13, 33, 49
44100	192000	(2/1)*(2/1)*(2/1)*(2/1)*(5/1)*(8/147)=640/147	479, 21, 13, 9, 31, 47
48000	8000	(1/3)*(1/2)=1/6	31, 449
48000	11025	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)=147/640	47, 31, 9, 13, 21, 479
48000	16000	(2/3)*(1/2)=2/6	31, 449
48000	22050	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)=147/320	49, 33, 13, 21, 475
48000	32000	(4/3)*(1/2)=4/6	31, 449
48000	44100	(147/8)*(1/5)*(1/2)*(1/2)=147/160	49, 37, 21, 469
48000	96000	2/1	431
48000	192000	(2/1)*(2/1)=4/1	449, 19
96000	8000	(1/6)*(1/2)=1/12	65, 449
96000	11025	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2) =147/1280	47, 29, 9, 9, 13, 21, 483
96000	16000	(1/3)*(1/2)=1/6	31, 449
96000	22050	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)=147/640	47, 31, 9, 13, 21, 479
96000	32000	(2/3)*(1/2)=2/6	31, 449
96000	44100	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)=147/320	49, 33, 13, 21, 475
96000	48000	½	431
96000	192000	2/1	431
192000	8000	(1/4)*(1/3)*(1/2)=1/24	25, 33, 461
192000	11025	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2) =147/2560	49, 29, 7, 9, 9, 13, 21, 487
192000	16000	(1/6)*(1/2)=1/12	65, 449
192000	22050	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2) =147/1280	47, 29, 9, 9, 13, 21, 483
192000	32000	(1/3)*(1/2)=1/6	31, 449
192000	44100	(147/8)*(1/5)*(1/2)*(1/2)*(1/2)*(1/2)=147/640	47, 31, 9, 13, 21, 479
192000	48000	(1/2)*(1/2)=1/4	19, 449
192000	96000	½	431

The converters are configured for chunk-by-chunk processing so that the resampling can be performed on arbitrarily large WAV files without incurring excessive memory usage. The delays introduced by the filtering are automatically removed so there is no need to separately compensate for the delays.

Since ReSample also includes a full range of re-quantization and dithering options, the WAV file can be completely re-sampled (in terms of sample rate and bit depth) in a single pass.