Return-Path: Received: (qmail 387 invoked from network); 28 Dec 2000 01:14:29 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 28 Dec 2000 01:14:29 -0000 Received: (qmail 13602 invoked from network); 28 Dec 2000 01:09:17 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 28 Dec 2000 01:09:17 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14BRQL-0007ol-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 28 Dec 2000 01:00:05 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from imo-r16.mx.aol.com ([152.163.225.70] helo=imo-r16.mail.aol.com) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14BRQK-0007o5-00 for rsgb_lf_group@blacksheep.org; Thu, 28 Dec 2000 01:00:04 +0000 Received: from MarkusVester@aol.com by imo-r16.mx.aol.com (mail_out_v28.35.) id l.22.fc6ccec (18255) for ; Wed, 27 Dec 2000 19:59:15 -0500 (EST) From: MarkusVester@aol.com Message-ID: <22.fc6ccec.277bea62@aol.com> Date: Wed, 27 Dec 2000 19:59:14 EST Subject: LF: Slow Voice with frequency offset To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="------------090205030502090409040002" X-Mailer: AOL 4.0.i for Windows 95 sub 70 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: This is a multi-part message in MIME format. --------------090205030502090409040002 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Dear Geri, Lionel, and LF group, playing with slow voice, I found that the main problem with simply time-stretching ("transposing") the audio spectrum is the slope of the transmitter's SSB filter. It is not steep enough to pass a lower band edge of about 75 Hz. One solution is to digitally shift the whole passband to the middle of the normal speech spectrum, eg. a 1/4-rate bandwidth of 1450 ... 2000 Hz above 1378 Hz zero beat. Such a function is not normally present in sound editing software, but by a combination of undersampling-aliasing and bandpass-filtering, an SSB mixer can be emulated. In the appended .txt file there is a description of how to (ab)use the GoldWave shareware sound-editor for this purpose. For receiving, you can reverse the procedure. An easier way for analog-minded people like me is to record the slow SSB signal from the RX (eg. Windows audio-recorder at 22050 samples per s), couple the PC's audio output to the antenna input of your VLF converter (tuned to 5.5 kHz USB, plus 4x any offset from the LF link), and replay the recording 4 times fast. Locally, the scheme worked amazingly well, now I'd like to try it out on the air. My preferred freq would be 136.88 kHz shifted zerobeat, 136.95 to 137.5 USB. With 16 mW radiated PEP this experiment will be rather restricted, so who of my neighbours would like to try? 73s de Markus, DF6NM --------------090205030502090409040002 Content-Type: text/plain; charset=windows-1252; name="SLOWVO~1.TXT" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="SLOWVO~1.TXT" How to produce time-expanded, frequency-compressed and passband-shifted SSB using the GoldWave sound editor by DF6NM, 26.12.2000 Basic principle: - start with 5512 Hz sampling, - equalize and filter, - resample to 22050 Hz causing aliasing around n*5512 Hz, - filter out USB spectrum above 5512 Hz, - reduce speed to 1/4. Working steps in GoldWave: Record voice using 11025 Hz sampling rate 1. 11025 sps 8bit -> 16bit 2. Lowpass 400 Hz (steepness 1, 6dB/oct to equalize sinc response of alias) 3. Bandpass 300...2500 Hz 3. (Volume *2) 4. Resample 5512 Hz 5. Resample 22050 Hz (causes the desired aliasing above 5512 Hz) 6. Bandpass 5800..8000 Hz (steepn. 20) 7. Volume *4 *4 *4 *4 8. Playback rate 11025 sps 9. Speed *0.5 10. Bandpass 1400...2100 Hz (steepn. 20) 11. (Volume *1.2 or nonlinear dynamics + Bandpass) 12. Save (8bit) Resulting SSB spectrum 1453...2003 Hz, zero beat 1378.12 Hz. Using Windows audio-recorder "sndrec32.exe" does not interrupt spectrogram while playing. --------------090205030502090409040002--