nero aac encoding shows conflicting sampling rates, 24000hz and 48khz

[uncertainty]

I'm using megui to encode my DVD collection using x264 for video and nero aac for audio (DVD source is 5.1 AC3 48khz). I have the nero config to not modify number of channels or sampling. The problem I'm trying to resolve is I am getting conflicting information regarding the sampling rate of the encoded 5.1 aac files. Mediainfo shows the sampling rate as 48khz which it should however afew of the media players I have (MPC Home cinema, Xbmc) show the aac file as 24000hz. I am including the logs from both Mediainfo and MPC Home Cinema. What program will show me the correct sampling rate if anyone knows?

Mediainfo log file

[Audio
ID : 2
Format : AAC
Format/Info : Advanced Audio Codec
Format version : Version 4
Format profile : LC
Format settings, SBR : Yes
Format settings, PS : No
Codec ID : A_AAC
Duration : 2h 44mn
Channel(s) : 6 channels
Channel positions : Front: L C R, Rear: L R, LFE
Sampling rate : 48.0 KHz
Resolution : 16 bits]


MPC Home Cinema AAC pin info

[Filter : AAC Decoder - CLSID : {3D446B6F-71DE-4437-BE15-8CE47174340F}

- Connected to:

CLSID: {0A68C3B5-9164-4A54-AFAF-995B2FF0E0D4}
Filter: G:\Movies\bridge.river.kwai.1957.dvd\bridge.river.kwai.1957.dvd.mkv
Pin: Undetermined (Audio 1)

- Connection media type:

Audio: AAC 24000Hz 6ch

AM_MEDIA_TYPE:
majortype: MEDIATYPE_Audio {73647561-0000-0010-8000-00AA00389B71}
subtype: Unknown GUID Name {000000FF-0000-0010-8000-00AA00389B71}
formattype: FORMAT_WaveFormatEx {05589F81-C356-11CE-BF01-00AA0055595A}
bFixedSizeSamples: 1
bTemporalCompression: 0
lSampleSize: 256000
cbFormat: 25]


thanks

[Keiyakusha]

I'm using megui to encode my DVD collection using x264 for video and nero aac for audio (DVD source is 5.1 AC3 48khz). I have the nero config to not modify number of channels or sampling. The problem I'm trying to resolve is I am getting conflicting information regarding the sampling rate of the encoded 5.1 aac files. Mediainfo shows the sampling rate as 48khz which it should however afew of the media players I have (MPC Home cinema, Xbmc) show the aac file as 24000hz. I am including the logs from both Mediainfo and MPC Home Cinema. What program will show me the correct sampling rate if anyone knows?

Your AAC has SBR, this means its encoded with AAC-HE profile. With encoding to this profile samplerate always halved and and its artificially restored on playback based on information, collected during encoding.
Edit: oops, I was faster ^_^

[menno]

This is due to the SBR used, it basically doubles the samplerate of the LC AAC part when decoding the file. So if you use a SBR capable decoder the file will be 48kHz, with an LC AAC only decoder it will be 24kHz.

[uncertainty]

Thank you for the quick reply. I checked the rev of my MPC Home Cinema player and it does indicate it decodes AAC HE+ SBR files. Do you happen to know how I can check to determine if the 24000hz is truely being decoded to 48khz?

thanks again

[Midzuki]

Do you happen to know how I can check to determine if the 24000hz is truely being decoded to 48khz?

You can try Graphedit --- place AC3Filter between the AAC decoder and the chosen audio renderer. The main tab of Ac3Filter has a read-only textbox named "Decoder Info".

[uncertainty]

You can try Graphedit --- place AC3Filter between the AAC decoder and the chosen audio renderer. The main tab of Ac3Filter has a read-only textbox named "Decoder Info".

I was able to enable the SBR decoding by disabling the MPC internal mastroka splitter and using the newer Haali splitter externally. It now shows the correct 48khz sample when playing. What a difference in the sound quality from 24khz to 48khz.

Thanks for all the help...

[FlipFlops2001]

The question is: Is the 24kHz readout sampling rate or audio frequency response?

In answer to the difference between 24k and 48k sampling rate not frequency response: 24kHz has an audio high-end limit of 12kHz, half of the sample rate, thus at a 48kHz sampling rate, the audio response will top off at 24kHz and sound better provided that the source was of good quality. There are other reasons why a higher sampling rate sounds better, but that's a whole other subject.