mad-dev September 2000

mad-dev@lists.mars.org

8 participants
15 discussions

Re: [mad-dev] MAD 0.11.2b available
by Andre McCurdy 18 Sep '00

18 Sep '00

Rob, Before I forget, there is something else I looked at a while ago which I haven't had time to explore more fully.... The distribution of values fetched from rq_table[] seems to be far from even (certainly for the few files I tested it with): rq_table[0] gets by far the most hits, rq_table[1] gets a few percent, with values after that dropping off fairly quickly. Based on this, maybe putting 'if (value == 0) return (0);' at the top of III_requantize() might give a (very) small speed up ? Also, by removing the first few entries from the table and recognising them directly it would be possible to fit the range of exponents in 4 bits rather than 5 and increase accuracy slightly. Any thoughts ?? Andre -- ____________________________________________________________ Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

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Re: [mad-dev] MAD 0.11.2b available
by Andre McCurdy 16 Sep '00

16 Sep '00

Rob, Thanks for catching my stupid mistake. Maybe it will teach me to read my own comments while fixing code rather than just using a regular expression search and replace... ! Your patch looks fine. Andre -- ____________________________________________________________ Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

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Re: [mad-dev] MAD 0.11.2b available
by Andre McCurdy 16 Sep '00

16 Sep '00

Nicolas, Well done for spotting the ARM 'Round while you shift' optimisation ! Originally in imdct_l_arm.S, I made a fairly arbitrary choice to round in some places and just shift in others to try and balance code-size/speed against accuracy. With your optimisation its possible to round everywhere with no penalty, so I guess it makes sense to do so. I've attached a new version to this email which hopefully should be the most accurate version so far - it now rounds everywhere like FPM_ARM and FPM_64BIT, but has the advantage over them of using 64bit accumulators for the imdct part. Rob, Just a small tweak: if ASO_IMDCT is defined, the window_l[] table in layer3.c doesn't need to be included (at a saving of 144 bytes....) as imdct_l_arm.S already contains its own copy. Andre -- ____________________________________________________________ Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

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MAD 0.11.2b available
by Rob Leslie 15 Sep '00

15 Sep '00

I put a new release of MAD on the FTP site. It's a day later than promised, but I wanted to incorporate some patches Nicolas sent me. This version has many changes. The highlights are: libmad changes: * Incorporated Nicolas Pitre's ARM assembly and parameterized scaling changes. * Incorporated Andre McCurdy's ARM assembly optimization (used only if --enable-aso is given to `configure' to enable architecture-specific optimizations.) * Reduced FPM_INTEL assembly to two instructions. * Fixed accuracy problems with certain FPM modes in synth.c. * Improved the accuracy of FPM_APPROX. * Improved the accuracy of SSO. * Added experimental rules for generating a libmad.so shared library. madplay changes: * PCM output is now dithered for better audio quality. * Added a resampling feature for unsupported output sampling frequencies. * Improved the OSS output module by falling back on 8-bit format if 16-bit is not available, and by using native 16-bit endianness. * Added a dual channel output selection option. The ARM changes produced a favorable effect on the accuracy of the output from libmad on ARM processors; ARM output is no longer the same as Intel output and instead now matches the 64bit output, but with better performance: default with SSO with ASO with SSO+ASO FPM_APPROX 6.800e-05/L 6.775e-05/L 6.431e-05/L 6.431e-05/L FPM_64BIT 5.580e-08/F 1.007e-05/L 5.652e-08/F 1.008e-05/L FPM_ARM 5.580e-08/F 1.007e-05/L 5.652e-08/F 1.008e-05/L FPM_INTEL 9.000e-08/F 1.008e-05/L /F means full compliance, /L means limited accuracy, /N means not compliant. Perhaps the most significant change to `madplay' is the addition of PCM output dithering. This is an alternative to ordinary rounding that improves the audio quality by reducing the negative effects of quantization noise. Dithering is commonly used in professional mastering when reducing studio-quality audio to 16 bits for pressing onto a CD. Since MAD produces PCM samples with >24 bits, dithering is a good idea. The dithered output sounds less "grainy" than non-dithered, although this is easier to perceive with 8-bit output than with 16. Best of all, however, dithering effectively increases the precision of the output because it allows bits below the LSB to be heard. There are many possible dithering strategies, but the chosen algorithm is fairly simple: it merely involves keeping the cumulative quantization error less than the significance of the LSB. The effect of this is for the LSB to modulate in proportional agreement with the bits below it. The only significant drawback with dithering is that it hinders an analytic examination of the output, such as compliance testing. Therefore, it can be turned off with a -d option to `madplay'. As always, the release can be found here: ftp://ftp.mars.org/pub/mpeg/ Cheers, -rob

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Re: [mad-dev] MPEG audio decoder compliance
by Andre McCurdy 12 Sep '00

12 Sep '00

Rob, Interesting. If you have them, I would also be interested in figures for MAD which compare multiplies using FPM_64BIT, a version which truncates the LSBit (eg FPM_ARM), and FPM_APPROX. Thanks Andre -- ____________________________________________________________ Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

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mad-dev September 2000