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Delayed RDS Data – Computer Time Lag

Skywaves wrote:

I have been using RDS Spy for this year's sporadic E season and it impresses me greatly. A brilliant piece of software.

I have a new problem however which has to be the fault of my computer. I am mentioning this here in case it is a problem for other users.

I have been trying meteor scatter but to no avail. I notice that it takes two seconds for the RDS data to appear in the RDS Spy window. Not much of a problem for sporadic E of course but not good for meteor scatter. There is an obvious time lag. I don't know if RDS Spy needs to be adjusted to compensate for this or if I need to adjust my sound card settings, which unfortunately are too complicated for me to understand.

Any advice or experiences appreciated.

Thanks

John
G1VVP

admin wrote:

Yes, there's a delay when decoding via sound card. But this delay is extremely important to allow continuous RDS decoding during the situations when Windows are busy. Windows are not real-time operating system so most accesses to hardware devices must be through a buffer.
There's a sound card buffer, it's size can be set in Options / General. The bigger buffer the longer delay.
Important fact must be noted: you don't lose anything! The reality is only one or two seconds delayed.

Skywaves wrote:

Thank you for the information.

My RDS Spy buffer is currently set to 64k. I could not get it to work with settings below this.

Sporadic E is fine with one to two seconds delay, but meteor scatter is seriously affected. I don't know how others are so successful, but there are other RDS Spy users who do very well indeed with meteor scatter RDS decodes. There is obviously something about my system which eneds to be looked at as meteor scatter is a no-go for me.

Thanks

John
G1VVP

DXer wrote:

If you can get 0% error rate on at least one station on the band, then your PC, sound card, buffering, RDS Spy etc. works correctly and the reason for the meteor scatter issue is elsewhere. Maybe you are down on luck for this time.

Skywaves wrote:

It does sound that way DXer. It's no big loss but it would have been nice to try MS DXing from my new location as the FM band here is so empty.

I was trying a few things yesterday and noticed that it can take five or six seconds before RDS Spy springs to life and produces the PI/PS information on its display, even with my strongest local transmitter. But, I don't think the problem is with RDS Spy, but somewhere with my computer since other DXers have excellent results with meteor scatter. Here's something else I noticed:

It's as if something on my computer is going into standby because the delay I experience occurs when RDS Spy hasn't received RDS data for several minutes. Once it springs to life, it is fine. I can then tune quickly to another station a seconds later and get an instant RDS display.

Thanks

John

admin wrote:

Let's compute:
buffer size 64 kB, sample rate 11025, stereo, 16 bit.
This is 44100 bytes/sec. Delay due to buffer: 64/44 = 1.5 seconds.
The delay can never be lower than 1.5 sec. when the buffer size is 64 kB! Of course, this is not the only one buffer in the path sound card – application.

However a delay of 5 seconds is something that I'm unable to resolve. Maybe if you post your actual wav record file from some audio editor, it will tell more. Maybe the Clock signal is not fed to the sound card so the RDS Spy synchronizes using Data signal only which may take some time. During this time you are losing information of course. As said before, if you can read 0% error rate on at least one station (and if Clock signal is correctly connected), then there's a delay but no information loss.

In the next version I'll probably add some status window where it will be clearly showed in what mode the RDS Spy operates and what signals are fed to the sound card.