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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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Kohlrabi
post Feb 27 2012, 21:50
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From: Kiel, Germany
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To assess the quality of a perceptual (lossy) encoder, please perform an ABX test instead of comparing spectra. MP3 is meant to perceptually reproduce the input audio file, i.e. achieve transparency. This means that the "missing" frequencies mean nothing if the resulting MP3 file sounds the same to you. It might also well be that most information in the higher frequencies might be inaudible or noise. If you want to archive your vinyl, use lossless encoding like FLAC or WAV. MP3, or any lossy codec, is meant for (end user) consumption.

This post has been edited by Kohlrabi: Feb 27 2012, 21:52


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