Daniel, In CBR mode, LAME in some ways ignores frequencies above 16 kHz, so not using a low-pass filter may allow more distorted signals at those higher frequencies (as opposed to mostly blocking the signals at those frequencies).
Considering this, and that only strange and very unusual experimental audio has audible frequency content nearly all the way to 22 kHz (the maximum storable frequency at the CD sampling rate), try guessing what removing the low pass will actually do. Many times, there won't be audible content over 19 kHz, so in these cases, the unfiltered sample will sound exactly the same as a sample with a low-pass at 19 kHz. (Okay, practically, that may not be true. The equipment will still try to produce frequencies that are inaudible, which eats power, and, depending on the equipment, could lead to distortion effects that trickle down into the audible frequency spectrum.) With VBR, LAME pays more attention to frequencies above 16 kHz, but due to a limitation in the MPEG layer-3 format, accurately preserving those frequencies may cost many more bits than it should. If your motivation for using "-k" is to attempt to preserve higher frequencies, you may find better performance with one of the VBR profiles than with CBR. However, at a given target bit rate, the excessive amount of bits sometimes required to preserve high frequencies may be better spent on the low frequencies instead. Many of LAME's VBR profiles already take this factor into account, and purposefully choose to partially ignore some of the high frequencies, and instead try to spend bits where there is a greater overall reduction in audible distortion per bit. You might find reason to use "-k" if the audio to be encoded has already been fed through a low-pass filter, or if you are dealing with lower sample rates, like 24 kHz, where the maximum reproducible frequency is quite audible. Here are some other questions that you might or might not care to look into, or that others might comment upon: With LAME, does "-q 1" offer better performance than "-q 0"? Is distrusting the joint stereo code and falling back to "-m s" worthwhile, considering the higher bit rate needed or possible loss of quality in other areas? At 320 kbps, if "-m s" is omitted, is spending the maximum bits per second still worth the incremental gain in quality, after considering the practical limitations of the encoder and MPEG layer-3 audio? Kind regards, - John Johnny Bravo wrote: > I am new to MP3 encoding. > > 1. What advantages / disadvantages does the command > "LAME -b 320 -q 0 -m s -k" have over "LAME -b 320 -q 0 > -m s". > > 2. According to the LAME version 3.91 MMX > (http://www.mp3dev.org/) manual > > -k keep all frequencies. (Disable all filters) > > -k will disable all lowpass filtering. Not > recommended. > > Does the "Not recommended" statement apply to all CBR > bitrates (including 256 and 320)? > > Many Thanks > Daniel X _______________________________________________ mp3encoder mailing list [EMAIL PROTECTED] http://minnie.tuhs.org/mailman/listinfo/mp3encoder
