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In Reply to: Re: Depends... posted by Christine Tham on November 04, 2004 at 12:41:02:
It states clearly how during the encoding process a difference data stream from the original 24/96 data stream is created by comparing it with the upsampled version from the downsampled core data.>>>
"The generalized concept of core+extension coding is illustrated in Figure 1. To encode 96 kHz LPCM the input audio stream is fed to a 96 to-48kHz down sampler and the resulting 48kHz signal is encoded using standard core encoder as in Figure 1 A). In the core+extension coding scheme that we first introduced in (4):• The core data is fed to a local core decoder whose output is up sampled in a 48-to-96kHz interpolator resulting in an interpolated core LPCM audio, denoted as signal “2” in Figure 1 A). Both operations are performed in the “Reconstruct Core Audio Components” block.
• In the “Generate Residuals” block the interpolated core audio is subtracted from the delayed version of input 96kHz LPCM audio (signal “1”) to generate the LPCM residual (signal “3”). The “Preprocess Input Audio” block performs the delay operation.
• The extension encoder (“Generate Extension Data” block) processes the residual LPCM signal and outputs the extension data. This data, along with the core data, is assembled in a packer to produce a core+extension bit stream.
<<<Above is describing encoder operation.
It's a bit like the following
Original data:
10 12 14 16 14 12 10 8After filtering and downsampling you get core data:
11 15 13 9Upsampling algo gives :
11 12 15 14 13 11 9 8Subtract from original gets extension data:
+1 0 +1 -2 -1 +1 -1 0Pack core data + extension data into dts stream
Decoding is fairly easy.
Standard DTS decodeer just decodes the core data.DTS9624 decoder decodes the core data. Interpolates it with the same algo as used in the encoder and adds the extension data.
It's an elegant solution.
The 48kHz core data is a decent downsampled audio signal.
The 96kHz reconstruction is augmented by the additional extension data requiring a lower bitrate. Difference data generally requires far fewer bits to encode.
Follow Ups:
... you probably did not realise this, but my post was agreeing with your view and in fact was trying to clarify it.i think you got so used to contradicting everything i say you don't even read what i post anymore, you automatically assume i'm criticizing you. of course, you are "usually" wrong and "deserve" to be corrected but that's another topic for another day :-)
I wasn't shure you understanded what I meant:> >
Frank is wrong (or at the very least misleading) when he suggests the core data decoding reconstructs "all" the samples. as we know, dts is a lossy encoder, so the reconstructed samples merely approximate the 48kHz stream.
< <I just tried to clarify that I didn't suggest what you wrote in the quote above.
*** It clearly indicates that the extension data is used to reconstruct all the samples in the decoder. ***No.
The extension data will never reconstruct *all* the samples, or even *any* of the samples. It's a lossy process, you never get back the original 96/24 stream. Only a close approximation.
I never implied a lossless process.My rough outline of the encoding process included the psycho acoustic lossy encoding of the 24/96 data as a first step.
It's obvious to all that information lost after that stage can never be reconstructed.
... that statement would still be wrong, when taken literally.Don't worry, Frank, I know what you meant (and I said so, remember?) I'm just teasing you as usual :-) No need to get into your usual "tortured justifications" :-)
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