:: Frank,
::
:: what's the reason to mess up the presets?
::
Original fm setting decreases FM quality by filtering out 10...15 kHz. AM
settings encode cross interference products instead of filtering them out.
:: a) with a highpass of 300 Hz you are loosing fundamental frequencies
:: of male voices (90-250 Hz)
:: FYI female: 160-500 Hz
:: kids : 200-800 Hz
::
Frequencies bounds are lowered to 200 Hz for phone and 100 Hz for phon+.
phone should be used to transmit the guranteed frequency response of the
telephone (300 Hz...3400 Hz, note that 300 Hz is suppressed by 6 dB!), phon+
for the possible frequency response: 0 Hz...4000 Hz. A high pass filtering
is recommened for low data rate transmissions, also it is recommended to
balance tonality of speech. 300 Hz is too high, that's right. I've changed
this value after CVS commit.
:: b) LAME's filter is not much useful for highpass filtering
::
External filters are available. For integration the f*cking "signed short
int" format must be replaced by "float" or "double".
I've heared (by listening) that the lame FIR high pass filter is not very
well. Extern 4th order butterworth filter are working much better. They also
can be used for Hifi highpass filtering (fu=30 Hz for records).
:: c) when you resample and want to lowpass, try to get rid off sfb21!
::
Can you explain this?
:: d) a steep lowpass results in ugly distortions, avoid this,
:: a round about 10-15 percent lowpass width sounds much better
::
AM low frequency settings: Cutting of cross interference products
is dimensions more important than preventing ringing.
And a dfo of 200 Hz is enough so you don't hear ringing.
phone/phon+/voice: no_short_blocks is set, so don't waste any second
about filter ringing.
For a fo >= 18 kHz filter ringing is inaudible. Also for dfo in the range
from 5...20 Hz (tested with FIR filters with orders around 10000, with
different persons and with different music). So I don't believe in the bad
filter ringing.
:: e) preset help text does not fit on 80x25 terminal anymore
::
Known. I'm searching for information about AM modulation bandwidth.
LW, MW, MW in USA and SW are different.
LW/MW df = 9 kHz, so filter should completely cut all above 4.5 kHz
SW: df = 10 kHz, so filter should completely cut all above 5.0 kHz
MW USA: df = 20 kHz, so filter should completely cut all above 10.0 kHz
Real frequencies are below this values.
I expect two sets: lw/mw/sw and mw-us.
:: f) VBR and CBR presets are out of sync now
::
For phone, phon+, lw, mw-eu, mw-us, sw and voice I've used three cabaret
pieces (mostly spoken words). CBR and VBR have nearly the same data rate.
For fm, radio, tape, hifi, cd and studio I've used ca. 30 minutes of music
(rock, classic, jazz). CBR and VBR have also nearly the same data rate.
May be I adjust this again in the beta phase.
--
Mit freundlichen Grüßen
Frank Klemm
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