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A few minutes ago I have uploaded an
experimental SlowVoice script to
The main purpose is to be able to convey high
quality speech in less than 800 Hz on the RF side, as prescribed by German
LF and MF regulations. By default, an audio band of 300 to 2700 Hz is
slowed by a factor of 3 and upconverted to 1500 Hz center frequency. Thus a
range of 1200 to 2000 Hz is fed to the SSB transmitter. As an aside
benefit we get a very much welcome 5 dB improvement in SNR.
Like JT9-1, the procedure is clock-synchronized in
fixed one-minute time slots. At the beginning of the minute, the transmitting
station is asked to speak for 20 seconds. It feels a bit like to
speaking to a telephone answering machine ;-) The slow converted output of
the growing audio buffer begins to play immediately, and will go on during
the whole minute. On the receive side, fast replay begins at second number 40,
and the shrinking buffer will finally be used up by the end of the
minute.
The SlowVoice.bat script is set up for full duplex
operation. One channel is supposed to handle the transmit side (eg. mic
connected to left input, transmitter to left output), while the other
channel has the receiver fed to the input and phones on the output.
This is symmetrical, and there is no further need to switch audio pathways
between TX and RX. It is also possible to monitor the result of one's own
transmission, eg. by physically connecting left line out to right in. If
you want you can use SpecLab in conjunction with Virtual Audio
Cable to preprocess both the mic and receiver audio inputs. In this case
VAC will have to be selected as the standard audio input device before the
running the script.
Whether a slots is used for TX or RX
is not controlled by the software but only by the user's PTT. I have included
two extra scripts which are supposed to activate the serial handshake lines
(RTS and DTR) on either even or odd minutes. Unfortunately the port
control does not seem to work on my XP machine with an external USB to
serial converter, so for the time being you may have to do with
either vox control or manual switching.
I haven't gotten around writing more detailed
instructions, but some basic hints have been included in the SlowVoice script.
Similar to the first slow WSPR experiments, the
whole deceleration / acceleration process is based on Wolf's sound
utilities which you will need to download from the DL4YHF web
site. You will have to run the included patch
utility once to duplicate SndInput and
SndOutpt instances.
Have fun! And please report bugs and other
troubles.
73, Markus (DF6NM)
----- Original Message -----
Sent: Sunday, January 06, 2013 1:50 PM
Subject: LF: Bandlimited SSB test on 136 kHz
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Slow voice transmission (ie the audio
deceleration/acceleration method originally used by DK8KW and myself) would
be nicer as it can fit a full SSB channel into 800
Hz. I have been working on a semi-automatic control, with a
fixed one minute raster similar to JT9-1. This will hopefully allow us to
comfortably exchange one 20 second voice message per time slot
(speak during seconds 0 to 20, concurrent transmit and receive at
1/3 speed from 0 to 60, replay starting 40 to 60). Anyone
interested?
...
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