MP3 解码器精度测试

MP3 解码器精度测试 ，集成现阶段所有解码器的精度分析。

测试结果来自MAD网站

MPEG Audio Decoder Compliance

Introduction

The purpose of this page is to share an objective analysis of various MPEG audio decoders, in particular the results of tests for decoder compliance with respect to the ISO/IEC 11172 international standard.

Decoder Compliance

Part 4 of ISO/IEC 11172 defines the compliance tests for MPEG-1 audio and video decoders. Section 2.6.3 defines the computational accuracy tests for audio decoders. It states:

To be called an ISO/IEC 11172-3 audio decoder, the decoder shall provide an output such that the rms level of the difference signal between the output of the decoder under test and the supplied reference output is less than 2⁻¹⁵⁄√12 for the supplied sine sweep (20Hz–10kHz) with an amplitude of −20dB relative to full scale. In addition, the difference signal shall have a maximum absolute value of at most 2⁻¹⁴ relative to full-scale.

Then it says:

To be called a limited accuracy ISO/IEC 11172-3 audio decoder, the decoder shall provide an output for a provided test sequence such that the rms level of the difference signal between the output of the decoder under test and the supplied reference output is less than 2⁻¹¹⁄√12 for the supplied sine sweep (20Hz–10kHz) with an amplitude of −20dB relative to full scale.

Thus, for the purpose of testing computational accuracy, we shall use three categories of compliance: fully compliant, limited accuracy, and not compliant.

Designations

ISO/IEC 11172-4 designates two kinds of audio decoders. Section 2.6.3 states:

An ISO/IEC 11172-3 compliant decoder that is able to support at least one but not all combinations of the options defined in 2.4.3 such as bit rates, sampling rates and modes, will be designated as an ISO/IEC 11172-3 Layer “N” audio decoder. Decoders that support all combinations are designated as Full Layer “N” ISO/IEC 11172-3 audio decoders, where “N” indicates I, II or III.

It should also be noted that, according to section 0.2 of ISO/IEC 11172-3:

An ISO/IEC 11172-3 Audio Layer N decoder is able to decode bitstream data which has been encoded in Layer N and all layers below N.

About the Tests

The following results have been obtained in tests conducted by Underbit in accordance with Annex A of ISO/IEC 11172-4.

All measurements are carried out relative to full scale where decoder output signals are normalized to be between −1.0 and +1.0. The supplied sine sweep with an amplitude of −20dB relative to full scale has an absolute amplitude of ±0.1 and a precision of 24 bits.

As instructed, where the output of a decoder is fewer than 24 bits, the remaining least significant bits are set to zero for purposes of normalization and measurement. (The number of output bits from the decoder is noted.)

Where the compliance test data contains two channels, or in the case of Layer II where multiple compliance test streams exist, the rms level and maximum difference values are calculated separately for each, and the greatest overall value used for the result.

Calculation of RMS

The rms (root-mean-square) level of the difference signal is calculated as

where t_i is the ith output sample from the decoder under test, r_i is the ith sample from the reference output, and N is the number of samples.

The maximum absolute value of the difference signal is simply the greatest value of |t_i − r_i|.

Test Results

Decoder	Bits	Layer I		Layer II		Layer III
		RMS Level	Max Diff	RMS Level	Max Diff	RMS Level	Max Diff
Floating-Point Decoders
amp 0.7.6	16	failed		2.099×10−5	3.421×10−5	1.959×10−5	3.362×10−5
				limited accuracy		limited accuracy
Amplay 1	16	failed		failed		7.860×10−2	1.487×10−1
						not compliant
Apollo 37	16	failed		2.099×10−5	3.421×10−5	1.961×10−5	3.529×10−5
				limited accuracy		limited accuracy
Audioactive MP3 Decoder 1.12	16	failed		failed		8.602×10−6	1.538×10−5
						fully compliant
CoolPlayer 7224 [Xaudio]	16	8.728×10−6	1.526×10−5	9.336×10−5	3.175×10−3	8.602×10−6	1.538×10−5
		fully compliant		limited accuracy		fully compliant
FreeAmp 2.1 beta 5	16	failed		1.408×10−1	2.259×10−1	1.410×10−1	2.003×10−1
				not compliant		not compliant
Jet-Audio 4.7 (64-bit float mode)	16	1.351×10−1	1.938×10−1	1.367×10−1	2.519×10−1	1.366×10−1	1.941×10−1
		not compliant		not compliant		not compliant
LAME 3.86 beta [mpglib]	16	failed		failed		8.870×10−6	1.836×10−5
						limited accuracy
maplay 1.2	16	1.738×10−5	3.052×10−5	1.850×10−5	3.052×10−5	failed
		limited accuracy		limited accuracy
maplay 1.2+ for Win32 1.A	16	8.728×10−6	1.526×10−5	9.996×10−2	2.659×10−1	8.602×10−6	1.526×10−5
		fully compliant		not compliant		fully compliant
mp3blaster 2.0b17	16	1.738×10−5	3.052×10−5	6.654×10−1	1.130×100	1.783×10−5	3.088×10−5
		limited accuracy		not compliant		limited accuracy
MP3 Decoder 1.45	16	failed		9.995×10−2	2.659×10−1	1.074×10−3	3.479×10−2
				not compliant		not compliant
MP3Player 1.23	16	8.728×10−6	1.526×10−5	8.759×10−6	1.526×10−5	8.602×10−6	1.538×10−5
		fully compliant		fully compliant		fully compliant
MP3 To Wave Converter 1.14	16	5.234×10−2	1.255×10−1	9.793×10−2	2.226×10−1	9.982×10−2	2.000×10−1
		not compliant		not compliant		not compliant
MpegDJ GoWave! 1.41	16	failed		1.854×10−5	3.779×10−5	1.780×10−5	3.064×10−5
				limited accuracy		limited accuracy
mpg123 0.59r	16	8.728×10−6	1.526×10−5	8.759×10−6	1.526×10−5	8.602×10−6	1.538×10−5
		fully compliant		fully compliant		fully compliant
MusicMatch Jukebox 5.10.0149 [Xaudio]	16	8.728×10−6	1.526×10−5	8.759×10−6	1.526×10−5	8.602×10−6	1.538×10−5
		fully compliant		fully compliant		fully compliant
NAD 0.94pb3	16	8.822×10−3	1.107×10−1	9.639×10−2	2.000×10−1	9.991×10−2	2.000×10−1
		not compliant		not compliant		not compliant
QuickTime 4.1.2, x86	16	failed		failed		8.602×10−6	1.526×10−5
						fully compliant
RightClick-MP3 1.65e [L3dec 2.72]	16	failed		failed		8.602×10−6	1.538×10−5
						fully compliant
Shibatch mpg123 plug-in 1.18+ for Winamp	16	failed		failed		8.854×10−6	1.836×10−5
						limited accuracy
Sonique 1.63	16	1.394×10−1	2.001×10−1	8.759×10−6	1.526×10−5	1.410×10−1	2.003×10−1
		not compliant		fully compliant		not compliant
Sonique 1.808 [audioEnlightenment 4.70]	16	8.981×10−6	1.836×10−5	8.994×10−6	1.895×10−5	8.867×10−6	1.836×10−5
		limited accuracy		limited accuracy		limited accuracy
Sonique 1.808 [audioEnlightenment 4.858 (Default Decoder)]	16	8.981×10−6	1.836×10−5	8.994×10−6	1.895×10−5	8.867×10−6	1.836×10−5
		limited accuracy		limited accuracy		limited accuracy
splay 0.8.2	16	1.738×10−5	3.052×10−5	1.863×10−5	4.232×10−5	1.783×10−5	3.088×10−5
		limited accuracy		limited accuracy		limited accuracy
UltraPlayer 2.00	16	8.965×10−6	1.824×10−5	1.262×10−2	1.297×10−1	8.854×10−6	1.836×10−5
		limited accuracy		not compliant		limited accuracy
Winamp 2.65 [Nullsoft MPEG audio decoder plug-in 2.33 (486)]	16	8.980×10−6	1.836×10−5	9.020×10−6	1.907×10−5	9.066×10−6	5.877×10−5
		limited accuracy		limited accuracy		limited accuracy
Winamp 2.65 [Nullsoft MPEG audio decoder plug-in 2.33 (Pentium)]	16	8.980×10−6	1.836×10−5	9.020×10−6	1.907×10−5	9.067×10−6	5.877×10−5
		limited accuracy		limited accuracy		limited accuracy
Winamp 2.65 [Nullsoft MPEG audio decoder plug-in 2.33 (MMX)]	16	4.524×10−5	1.634×10−4	4.539×10−5	1.811×10−4	9.067×10−6	5.877×10−5
		limited accuracy		limited accuracy		limited accuracy
Winamp 2.666 [Nullsoft MPEG Audio Decoder 2.666]	16	8.727×10−6	1.526×10−5	8.759×10−6	1.526×10−5	8.602×10−6	1.526×10−5
		fully compliant		fully compliant		fully compliant
Xaudio 1.1.0, x86 [decoder library 1.3.1]	16	8.728×10−6	1.526×10−5	8.759×10−6	1.538×10−5	8.602×10−6	1.538×10−5
		fully compliant		fully compliant		fully compliant
Integer Decoders
Intel® IPP 1.01, StrongARM	16	failed		failed		8.631×10−6	1.812×10−5
						fully compliant
MAD 0.11.4b, ARM	24	4.667×10−8	2.384×10−7	4.906×10−8	2.384×10−7	5.338×10−8	2.384×10−7
		fully compliant		fully compliant		fully compliant
MAD 0.11.4b, x86	24	6.198×10−8	3.576×10−7	6.198×10−8	2.384×10−7	9.000×10−8	9.537×10−7
		fully compliant		fully compliant		fully compliant
MAD 0.11.4b, x86 (optimized for accuracy)	24	4.667×10−8	2.384×10−7	4.906×10−8	2.384×10−7	5.555×10−8	2.384×10−7
		fully compliant		fully compliant		fully compliant
MAD 0.11.4b, x86 (optimized for speed)	24	7.131×10−6	2.480×10−5	7.250×10−6	2.789×10−5	7.227×10−6	2.730×10−5
		fully compliant		fully compliant		fully compliant
mpg123 0.59r-arm32	16	6.972×10−2	1.000×10−1	7.058×10−2	1.300×10−1	7.051×10−2	1.001×10−1
		not compliant		not compliant		not compliant
splay 0.8.2-fp1	16	2.180×10−5	6.604×10−5	1.961×10−5	4.458×10−5	5.618×10−2	1.190×10−1
		limited accuracy		limited accuracy		not compliant
Xaudio 1.1.0, ARM [decoder library 1.3.1]	16	6.945×10−2	9.965×10−2	2.003×10−5	3.576×10−5	2.065×10−5	6.580×10−5
		not compliant		limited accuracy		limited accuracy

Legend
fully compliant	The rms level of the difference signal is less than 2−15⁄√12 (≅ 8.810×10−6) and the maximum absolute value of the difference signal is less than or equal to 2−14 (≅ 6.104×10−5).	The decoder is an ISO/IEC 11172-3 Layer “N” audio decoder.
limited accuracy	The rms level of the difference signal is less than 2−11⁄√12 (≅ 1.410×10−4). (The maximum absolute value of the difference signal does not matter.)	The decoder is a limited accuracy ISO/IEC 11172-3 Layer “N” audio decoder.
not compliant	The rms level of the difference signal is greater than or equal to 2−11⁄√12 (≅ 1.410×10−4).	The decoder is not a compliant ISO/IEC 11172-3 Layer “N” audio decoder.
failed	The decoder failed to produce output for the given test bitstream.	The decoder is not a Full Layer “N” ISO/IEC 11172-3 audio decoder.

Notes

Full Compliance

It should be noted that a fully compliant result from these tests does not mean the decoder in question is without flaws.

These tests only verify the computational accuracy of decoders against a reference signal that spans only 20Hz–10kHz of the frequency spectrum. While this test may be enough to detect a problem with a decoder, it is not enough to certify that a given decoder will correctly reconstruct frequencies outside this range, or that the same decoder will correctly handle any valid bitstream. To obtain these kinds of assurances, further tests are necessary.

Quantization Method

It should further be noted that these test results can be affected by the method used by each decoder to quantize its PCM output. Some decoders may use dithering or noise shaping to reduce the negative effects of quantization noise and improve the perceived audio quality, while others may simply round each output sample to the nearest integral value. Unfortunately, with few exceptions, it is not known what quantization method is used by each of the tested decoders.

It is possible for an otherwise fully compliant decoder that implements dithering with 16-bit output to appear only to have limited accuracy. The decoder’s outputbefore quantization should be the true measure of its accuracy.