[Lf] Speeding up QRSS CW]

[Andre' Kesteloot]

Lionel Sear wrote:

> The recent correspondence on Slow-Audio is of interest to me as it would
> need techniques very close to those I have been using with the PC/soundcard
> combination to receive slow Morse.
>
> I am using FFT/inverse FFT filtering to filter signals in the 1000Hz region
> through selectable bandwidths from 30 down to 4 Hz. To speed up a signal 16
> times I then transpose the signal down to one sixteenth of the frequency
> and then take an average of successive groups of 16 samples which restores
> the pitch back up to the original, and then stores this in a .WAV file. It
> is thus possible to record 1 wpm CW and play it back at 16 wpm and at the
> original pitch. Speed-up factors of X2 to X16 are available.
>
> This program is at an early stage but if anyone would like to have a play
> then download:
>
>                             http://www.lsear.freeserve.co.uk/qrss.zip
>
> The program runs under Windows95 and requires a modest PC with a soundcard.
> It is at an early stage but has been tested on 80m between myself and G3SMC,
> and also KF4HEY has some ongoing tests using simulation software. It works,
> but I cannot guarantee that it will outperform the skillful use of the
> waterfall display. However, it may be that under some conditions the ear may
> be better than the eye. One slight problem occurs with some selected
> frequencies where the audio blocks do not join up seamlessly and give a
> clicking on the audio.
>
> As far as slow audio goes, I wonder if it would be possible to record 2 kHz
> bandwidth  speech into a .WAV file at 44100Hz and then alter the sampling
> frequency in the file header to 11025Hz. Playing this would result in the
> speech with a duration four times as long but in one quarter the bandwidth.
> The frequency band would span 1 to 500Hz, so this would need to be
> transposed up to 300-800Hz in order to go through an SSB filter. Reception
> could be by similar techniques to those used in QRSS.EXE referred to above
> but with a further transposition to restore the original pitch. With the
> SB16 card, it would be possible to play a .WAV file at 5513Hz though a 250Hz
> bandwidth  but not all soundcards allow the choice of non standard
> frequencies.
>
> Sorry about the long email, but I think it worth mentioning that I was in
> the LF group at the start of things and became interested in the DSP aspect,
> indeed it was Andy Talbot's suite of PowerBasic programs that gave me a
> start. The DSP bit took me off at a tangent and I have spent the intervening
> time developing programs for Hellschrieber and MFSK. One development,
> SLOWFELD.EXE, where FFT bins are plotted as the individual pixels in a form
> of Hellschreiber running at 2 characters/minute, would I humbly suggest, be
> ideal for LF use, since it gives a bandwidth of 2Hz. Take a look at:
>
>                  http://www.lsear.freeserve.co.uk/slowfeld.zip
>
> Again it uses a PC/soundcard with Windows95 but it allows for the on/off
> keying of a simple Tx as well as outputting audio for SSB. Maybe it has been
> tried on LF but I have had no confirmation of this
>
> 73
> Lionel
> G3PPT