Out of concern and curiosity, I decided to measure my TX Latency from mic input or VAC input through PowerSDR. to the TX I & Q signals. The hardware: SDR-1K, AMD 3300+ CPU 1gb ram (CPU utilization < 10%) , on board sound card, D44 sound card & Ozy/Janus sound card. The software: PSDR 1.10.3, Audacity 1.2.5, VAC 4.08 With external cables and 'Y's, I setup Audacity to capture the mic input to PSDR on Left stereo channel and the PSDR TX I output on the Right stereo channel. I then recorded brief transmissions with Audacity and measured the delay between the left channel (mic/VAC) the right channel (TX I or Q).
In the first test series I measured delay for the O/J mic input to O/J TX I output. For the second series I measured delay for D44 mic input to D44 TX I output. Mode LSB,VAC off, 48000 BPS sample rate Sound Card SC buffer DSP buffer delay O/J 2048 4096 270 msec O/J 2048 256 120 msec O/J 256 256 40 msec D44 2048 4096 310 msec D44 2048 256 160 msec D44 256 256 Failed. (no signal through put ) For the VAC port latency tests, in the PSDR VAC setup form, I selected the D44 3/4 sound card as the input ( no VAC cable ), the measured delay was therefore from the D44 mic input, through the AC channel of PSDR and out the O/J TXI/Q. Mode DIGL,VAC on, 48000 BPS sample rate VAC-O/J 2048 4096 320 msec VAC-O/J 2048 256 155 msec VAC-O/J 256 256 190 msec VAC buffer size seemed to have little effect on latency for this test. Immediately AFTER toggling TUNE ... VAC-OJ 2048 4096 2450msec ( yes 2450 msec ! ) (toggling VAC restored original measurement.) Next I included the actual VAC software (v 4.08) in the latency test. In this test I routed the test signal through the D44 3/4 sound card, an audio repeater, and a VAC channel to the VAC input of PSDR and out to the O/J TXI/Q. VAC-O/J 2048 4096 900 msec VAC-O/J 2048 256 450 msec VAC-O/J 256 256 390 msec Again the VAC buffer size seemed to have little effect on the TX latency. Disclaimer... This is a sample of 1.. Different CPU's will have different latency... Small buffer sizes have other (undesirable ? ) effects. I would be interested in hearing other measurements. YMMV AL, K0VM _______________________________________________ FlexRadio mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
