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Old 05 October 2005, 10:58 am   #1
Q-W-Y
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Default mpc cuts off high frequencies?!

I've done spectral analyse of source FLAC file and decoded mpc - when using --insane profile, there is cut at 19kHz ..
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Old 05 October 2005, 11:20 am   #2
cane
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Well, if the psy-model decides that it can't "hear" frequencies above 19khz in certain passages, to me it seems perfectly normal for it to cut off those frequencies.

As you can see from the 'Insane' profile definition, the maximum encodable bandwidth is set to 22khz.

Code:
 SV 7.0 + XLevel coding, Profile 'Insane'

 PCM fader                : fade-in: 0.00 s, fade-out: 0.00 s, shape: 1
 Scaling input by         : left 1.00000, right: 1.00000
 Maximum encoded bandwidth: 22.0 kHz
 Adaptive Noise Shaping   : max. 6th order
 Clear Voice Detection    : Dual
 Mid/Side Stereo          : Mid/Side Stereo when superior + enhanced (3/12 dB)
 Threshold of Hearing     : Model 570: min(Klemm,Busch), Max ATH: 64 dB, Offset:
 -12 dB, +Offset@20 kHz:-12 dB
 Noise masks Tone Ratio   :  9.5 dB
 Tone masks Noise Ratio   : 24.0 dB
 Exploitation of temporal post masking
 Minimum Signal-to-Mask   :  3.0 dB
 No deleting of input file after encoding
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Old 05 October 2005, 02:22 pm   #3
Kamen
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Most people are unable to hear these frequencies and the psychoacoustic model of MPC is designed after this. Cutting off and masking is something normal which our ears do and of course it can be seen with a FFT analysis, for example. Musepack just emulates our psychoacoustics. All these things are a part of the psychoacoustic model, which is perfectly adjusted, so the ear cannot notice differences in quality. The bandwidth switch sets the maximum frequency which can be encoded, but doesn't "enforce" the encoder to always encode up to that frequency. This switch is just a lowpass filter. The ATH determines the real bandwidth. To increase the bandwidth, if you are so pedant and want to keep these high frequencies, then you can change some settings manually. Increase the negative value of the HF offset. Changing other options like --ltq_gain (overall ATH offset) and the masking thresholds is not needed.
Generally, using values around the BrainDead profile and above will give you the same spectral picture as FLAC, but it isn't needed and in most cases even a sensitive ear won't notice anything.
So I can say, though MPC is a lossy format, you lose nothing.

Last edited by Kamen; 13 July 2009 at 10:15 am. Reason: corrected spelling mistakes and outdated information
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Old 05 October 2005, 03:28 pm   #4
Q-W-Y
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oki, thank you ppl :P
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