Topband: CW Speaker Mystery - My Experience

[n4is at comcast.net]

Hi Peter

Thanks for the nice recordings. I will check with my CW speakers. I learned a lot of new things playing the 9M6NA  CW signal recordings. Just for sharing my notes, long notes, sorry for that.

1- SDR radio D/A converter also introduce noise, intermodulation and the signal to noise ratio is proportional to the price you pay. Some called them DAC. Resolution is important, like 192K/32 bits has more resolution than 96K/16 bits. Well,  price talks, the DAC used on our popular radios are not the same. My main radio is an IC-7851, there are 3 main audio output, each one uses a different DAC. the phone output on the front panel, the   DAC has near 100 db SNR and 120 DNR, and the DAC for the speaker output on the back has only 80 db SNR and 100db DNR, DNR is dynamic range, The IC7850 has both DAC with 120db DNR and was much pricier!
Price talks the ICOM save some money with a not so good DAC for the speaker output. Another important fact is the THD is also different. The best way to get a better signal to noise ratio out of the IC-7851 is the S/PDIF output. The digital signal can be converted using a good external DAC with 140db DNR. My audio panel has a DAC with S/PDIF input and, 32K-192KHz SNR: ＞120DB, Dynamic Range: ＞120DB and THD + N : -107DB. Here you can spend U$50 to U$ 5000 on audiophile DAC,  I paid U$20 few years ago :
https://www.ebay.com/itm/353414734553
These are good enough. Imagine you situation working a weak signal  (-130 dBm) covered by the noise and intermodulation from the DAC. Remember noise is basic temperature noise, db is just a number, simple math does not apply here. The audio intermodulation noise plus weak signal is another issue.

2- Using a high-quality DAC like the USB external Sound BlasterX G6 sound card on my PC. I noticed the problem with audio intermodulation. The G6 has an excellent performance for the price. 32-Bit / 384 kHz 130 dB DNR. Here the tests results.
I started to test the CW speaker playing the HPSDR RF recording using a good quality PC speaker. The weak signal was Q5 on the cw speaker and just noise on the PC speaker. I recorded the experiment using my iPhone. Playing the video, I learned that the DSP on iPhone notch off the CW signal, like removing eco or noise, the signal from the CW speaker just was not recorded. The same happened during 3 club meeting presentation, the local guys heard the cw from the CW speaker but not the remote guys on ZOOM meeting App. The DSP was optimized for voice, and not a single frequency. It  is just noise for the DSP on the ZOOM app.
Here is the main discovery. I have a HiFi amplifier and HiFi speaker to listen to Jazz connected to the G6 DAC, all that jazz!. I played the same recording on the HiFi system and for my surprise, I was able to copy much better the same recording on the HiFi system. Yes, the noise was the same, but the signal was copyable. The CW speaker was better SNR than the HiFi,  and the HiFi was better than the PC speakers. Conclusion the noise and TDH on the audio amplifier does impact the copy of the weak signal. PC speaker system amplifier/speaker have very limited performance.

3- Audio intermodulation is something I don’t understand very well, it is not only THD, when you have the signal below noise level the audio quality is not the same when the signal is above noise level. May be Jim can help me here. 
Audio amplifier with low noise at the low power level we need for CW copy is a challenge.  Performance at high power is not the same for low power, in the same amplifier. One good amplifier you can found here. Ultra-low distortion amplifier at low cost, at low power < 1W.

https://www.kaltecs.com/32w-ultra-low-distortion-kit/

Difficult to understand but you can copy the weak signal using one audio amplifier and do not copy the same recording on a different audio amplifier, using the same speakers.

Same thing with our loved headphone!  The difference here is unbelievable. Last year I bought a Beyerdynamic DT 880 600 ohms. I have a Beyerdynamic DT 770 PRO 250 Ohm
I was having fun working a SSB contest on 160m, and I heard a PY3 very weak on SSB using the 600 Ohms headphones, then I switched to the 250 ohms, and I could not understand the same station, the difference between understand and not, is it a question about clarity ? Jim, can you help me here to understand why so much difference between to good headphones. The same results hearing he 9M6NA CW recording,  clear difference using the 600 ohms headphones from the  same maker.

4- Psychoacoustic is real. Psychoacoustics is the scientific study of how humans perceive sound, including the psychological responses to different sounds like noise, speech, and music. It combines elements from psychology and acoustics to understand how sound waves are interpreted by our auditory system and how they affect our emotions and experiences. Each of us are different and alike at the same time.
However electronic circuits are not the same at all, even with the same names.
I like to experiment with audio and build my own speakers since I and a teenager.

I know FT8 does not have all the above, or it does, I don’t work FT8 so I don’t, know.

73's
N4IS
JC