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missing frequencies/sounds >16kHz using lame 3.99.4-64
shmick23
post Feb 26 2012, 14:51
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hi,

i recorded some vinyl using Goldwave 5.25 under win 7 pro x64 and saved the files as a 24/96 un-compressed Windows Wave file.

i had a look at the frequency representation in Adobe Soundbooth CS5 and noted that the max. freq. attained was around ~27kHz (which seems acceptable given my sound card, cartridge and phono stage).

i then compressed the file using Foobar2000 1.1.9 to a lame mp3 with the settings:

Audio
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Mode : Joint stereo
Duration : 5mn 51s
Bit rate mode : Variable
Bit rate : 282 Kbps
Minimum bit rate : 32.0 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Stream size : 11.8 MiB (100%)
Writing library : LAME3.99r
Encoding settings : -m j -V 0 -q 0 -lowpass 24 --vbr-new -b 32

having a look at the frequency representation again in Soundbooth showed a reduction/cutoff above 16kHz for certain sounds (not all).

Why is this and how (if possible) could I retain these upper frequencies ?
I assumed since the mp3 is a 48kHz file each channel should contain up to 24kHz sounds - from the graph it does, but only for certain sounds, and others are removed >16kHz

Also, is it a default setting by either foobar/lame to use lowpass by default ?

i've uploaded some screen grabs for visualisation:










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[JAZ]
post Feb 26 2012, 15:54
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From: Catalunya(Spain)
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What you see in action is the "ATH". As you know, MP3 is a lossy encoder, and as such, it decides to hide and remove sounds (or simply replace it by something that "sounds" alike).

Also, the MP3 as a format, has more difficulty storing the frequencies above 16Khz with precision. LAME, in order to preserve better the whole sound, tends to be a bit more aggressive on the higher end of the spectrum, provided that the sound is below the ATH. (which translates to "the quietest frequencies").

In the end, this appears graphically as this sort of dynamic filter above 16Khz.

Also, you shouldn't be using --vbr-new with 3.99. --vbr-new was made default in 3.98, and in 3.99, --vbr-new stands for a new setting which is in development.
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