Contest Audio Recording

A few years ago I made a simple headphone splitter to feed the TS-850 headphone output back into the line input of the PC’s sound card. Why headphones when the TS-850 has a fixed volume / fixed impedance line output? Because this output only offers RX audio and mutes on TX. At least that’s what I remember. It has been so long ago. Hence the headphones output, that also has my TX signal.

With this simple setup I could record some nice DX QSO or other people’s interesting operating techniques. Some ON4 calling ZF2NT on 40 for 12 minutes in ARRL DX CW, a classic in ON5ZO’s archive. Or working my first zone 3 on 80: K6NA, December 2003. A loud and clean recording mailed to K6NA after sending $$$ for a QSL in vain… Never seen a card nor a reply to my email. But I digress.

Later on I installed the MK2R+ SO2R controller which replaces the PC’s sound card. I didn’t really find a way to record the audio with the MK2R+. It should be possible, I tried looking for a way including the reflector but since it wasn’t high priority, I abandoned the search. Before CQ WW SSB, several people (like Mike SJ2W) asked to send in some sound files with their signal. I always like to hear how I sound too. CN2R and K5ZD offer post-contest audio. Always a sobering experience. So I decided to give it another go and record the whole contest using RecAll Pro. This program lets you record a long period in different files and sizes.

I did not want to stress the contest PC so I used my old laptop to record the audio. I could use it’s line in but where to get the RX audio? The MK2R+ strangely enough does not have an auxiliary audio output. Or did I miss it? So back to splitting the headphones output? Then I remembered the K3 has an external speaker output. This would only offer SO1R audio but in WW SSB I wasn’t using the second TRX.

A quick ‘proof of concept’ was successful. However the audio does not sound clean. Here’s why. I have a professional broadcast headset in which I placed the Heil HC4 mic capsule. The real Heil headset is way too expensive in my opinion and the broadcast ear shells really block all outside noise. Best of both worlds: Heil audio and no external sounds. This headset has high impedance speaker elements. As a result of Ohm’s law and a higher impedance, I need to crank the K3’s volume up for RX audio as well as TX monitoring. Since the external speaker’s output follows this cranked up audio gain setting, a strong and overdriven signal is injected into the laptop’s line input. Hence the loud and distorted audio recording.

I could make a simple resistive attenuator to reduce the signal fed into the laptop. But I think the only way to solve this and have SO2R audio on the recording is to use the MK2R’s headphones output. There are two options for this. A simple passive split like before, soldering headphones and sound card in parallel. Or use my professional Behringer PowerPlay distribution amplifier (yes I have a history in the broadcast industry 🙂 ). The benefit is that I can independently set the volume for headphones and recording level. The downside is yet another device I need to give a place, and increased chance of RF QRM pick up.

There also is a problem with the transmitted WAV files on my new Win7 x64 machine. When I log a QSO, N1MMLogger sends my ‘thank you’ WAV file. At the same time, it writes the contact to the database and does a rescore. I think this rescoring takes up quite some CPU resource. Remember: the new PC is not really new but almost 4 years old. The CPU resource monitor shows a short and modest burst (20%). The result of this is that “Thank you oscar quebec five mike” rolls out like “*hiccup stutter* you oscar quebec five mike”. All other sounds roll out just fine, as long as there is no computation done. I listended to the recordings and it bothers me a lot. I pay a lot of attention to these details and this makes me sound like a LID. I never had this stuttering on my other PC. It might be a Windows issue (7 vs XP) or a hardware issue (AMD / Asus MB combo versus Intel / Asus). I already have some clues but I need to run some tests. If it is indeed a hardware latency problem on the older CPU / main board combination, I guess it’s time to buy a new motherboard and Intel CPU.

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