An Audio QSO Recorder with Instant Playback

14 Jul 2021 - Jim Evans, G3VDB

I searched for an audio recording program that would record continuously but allow me to replay repeatedly the last few seconds of the recording. I wanted this for Radio Contests. If I misheard some exchange, I could immediately replay the audio, if necessary several times. Not finding such a recorder, I wrote one. I modified an audio recording example from the CSCore Audio library. As you might expect, the first attempt has limitations. It can be improved.

Background

It has been the bane of my Radio Contesting life that I start to fill in the log only to realise I have failed to absorb some important aspect of the exchange. Something goes wrong with serial numbers or (in VHF contests) the reports or locators / QRAs. Either I did not write down some item clearly (VHF) or I entered the information correctly but 'finger trouble' cleared out the data rather than saving it. In a recent CW contest I wiped out a valid QSO before logging it; I then had to guess the serial number received. Luckily I got it right but…..

Years ago I might have gone through a recording after the contest to complete the log; that is no longer within the rules, nor within the spirit, of the modern test. Any changes to the log should be made during the period of the contest.

For some time I looked for software that would record the last few minutes of audio and allow you to quickly replay the last QSO to restore the missing info during the contest. Most logging software has recording capabilities; Modern rigs can also record the rig audio. l could find lots of software that would record the whole contest or would record for a few seconds and then stop (HRD) but I couldn’t find anything that met my needs, which would

• record continuously to disc with the most recent audio kept in memory too.
• Have a button to grab and hold onto the last several seconds.
• Let you repeatedly play a portion of that “grab” while recording continues in the background.

The Result

By modifying the simple recording example within the open source CSCore audio suite, I now have something that works.

• It records continuously to a named .wav file
• By clicking a button, it copies, or grabs, the last one minute of audio to a buffer (but it could be longer or made variable).
• You can repeatedly replay the end of this grab, until you grab another last minute. The replay length is the last 5 to 60 seconds; the length is selectable in 5 second steps.

It should be useful in Voice and CW contests on any band though unlikely to be of use in data contests without some modifictions.

Limitations

In this proof of concept version

• settings are not saved
• the grab function is fixed at the last one minute
• replay is to the Windows default soundcard output.

The last point is a disadvantage. When contesting you are almost certain to be listening to the radio with headphones. To have the replayed audio coming out of PC speakers or headphones is not satisfactory. There are options:

1. Change the program to feed the radio audio through the PC sound card, muting the radio feed during playback of the recorded sample.
2. Use an external Y-cable to combine the two feeds to one set of headphones. You’d have to mute the radio manually during playback.
3. Design a simple hardware audio combiner / switch to achieve the effect of 2.

For a software developer, option 1 is preferred, provided the inevitable delay introduced is small and acceptable in a contest environment.

If you think you might have a use for this, then let me know. There is an installation package available for WIndows 10 and 7. There is a cursory description of use (and its current limitations) as a .pdf file. If you know anyone who might be interested pass the message on.