[Mp4-tech] Re: MPEG-4 Audio Conformance...problem with reference Wavfiles ?

[Ralph Sperschneider]

Umang Garg wrote:
> Dear Members,
> 
> Can someone please corroborate if the reference Wav files for AAC-LC 
> kept on the following FTP fite
> 
> ftp://mpaudconf:adif2mp4@ftp.iis.fhg.de/mpeg4audio-conformance/referencesWav 
> 
> 
> have problem in their header !
> 
> Example Problem:
> 
> al01_48.wav:
> The byte numbers 20 in this file contains the value 0xFE while the byte 
> number 21 contains the value 0xFF.
> If I am not wrong then according to the Wav PCM Format, byte number 20 
> and 21 represent the AudioFormat.
> For PCM(linear quatization) this value should be 1. Hence, the correct 
> value for byte 20 should be 0x01 and for byte number 21 should be 0x00.
> 
> Due to this problem we can not play these Wav files in the CoolEdit and 
> also in the RealOneplayer.
> 
> 
> These comments also hold true for various other al*.wav files in the 
> directory 'referencesWav' on the aforesaid FTP site.
> 
> 
> Thanks and Regards,
> 
> Umang Garg
> 
> 
> NeoMagic Corporation, based in Santa Clara, California, provides 
> applications processors to enable new generations of handheld Internet 
> systems, offering the lowest power, smallest form-factor, and best 
> multimedia features and performance. The company has pioneered the 
> integration of complex logic, memory and analog circuits into 
> single-chip solutions. NeoMagic is mobilizing multimedia for the 
> Internet age. Information on the company may be found on the World Wide 
> Web at www.neomagic.com.
> 
> 
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Dear Umang,
I already stated some time ago in an e-mail from me to this reflector:
"
Have you tried to play the waveforms with the Windows MediaPlayer? This should 
work. The files are in 24 bit wav format as specified recently by Microsoft. 
Before, there was no standard but just a pro-forma standard. Unfortunately, 
Microsoft did not use that pro-forma standard, but changed some header bits. 
Thus, many audio tools cannot yet handle this format.
"
BTW: Newer versions of CoolEdit 2.x) should be able to read those files.
Please find below a more extensive info from Peter Kabal, the creator and 
maintainer of the AFsp library:
 >> Microsoft has never recognized 24-bit files created using the WAV
 >> standard even though the standard quite clearly indicated that one could
 >> use bit depths greater than 16.
 >>
 >> Recently, Microsoft introduced an "WAVE_FORMAT_EXTENSIBLE" and has
 >> declared: "WAVE_FORMAT_EXTENSIBLE shall be used whenever the PCM data
 >> has more than 16 bits" or the number of channels is more than 2".
 >> Programs such as Microsoft Media Player will not accept 24 bit files in
 >> the older format, but does accept them in the newer format.
You might also read about the details here:
http://www.microsoft.com/whdc/hwdev/tech/audio/multichaud.mspx
Best regards,
Ralph
-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
FhG IIS                         | Fax:   +49 9131 776 398
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