I was thinking about this yesterday. What is my MDS, minimum discernable audio signal? At 66 I likely hear less than someone at 46, on average. My Baldwin phones likely limit me too, not matriculated to SP yet. I think I'll use my generator at audio freqs and measure what I can hear with the Baldwins property matched. Might even have my hearing tested - hear ok; but primary to see what the pros say/do it. Anybody done this?

An aside. Should we get extra points in contests for depreciated hearing? Or, saying it another way, should we get an amplifier "permit" to adjust our hearing to that of a 20 year old? HM?

Phil, WØXI

"One should never increase, beyond what is necessary,
the number of entities required to explain anything." What Would Maxwell Say [1831-1879]

The bandwidth needed to copy CW is only a small portion of that needed for AM. I can easily copy CW in a bandwidth of 400 Hz, and usually down to less than 100 Hz (although it's not easy to get such narrow filters, since they tend to ring). AM requires at least 3 KHz for communications quality, and music requires quite a bit more.

You definitely do need an adequate signal, or, perhaps, that should be restated that you need an adequate signal to noise ratio.

You also need a demodulator. For AM, that can take the form of a diode, or it can be more complex (e.g., synchronous detector?). For CW, you usually need the BFO (more on this later).

As for needing the human ability to hear, that's not really necessary for CW. I've known some individuals over the years who can copy CW optically (e.g., reading a flashing light) (in which case, the need for the BFO
goes away). There may also be other channels which make it possible to copy CW (e.g., sense of feel to copy CW), although I've not personally known anyone who has used those channels.

As you age, your hearing usually declines, usually by narrowing the bandwidth that you can hear, but there may be a decrease in sensitivity, too. I know that I used to be able to hear the 15,750 Hz audio from a "singing" horizontal output stage in a television, but I can no longer hear that (I'm down to a upper limit of about 13 KHz now.).

I've had some professional/medial hearing screenings over the years. They didn't really tell me anything that I didn't already know (although I would recommend it to anyone who may suspect they have an abnormal hearing loss, or who is having trouble hearing). Note that there are signal generators available for PCs that will let you specify the volume and frequency of a sound, so you could perform your own hearing test (However, do not use these for medical diagnosis purposes! For that, you need consultation with a doctor/audio specialist.).

As for an amplifier for some of the crystal radio contests, I assume you're talking about something other than a hearing aid. On the other hand, what are the rules with regards to hearing aids?

Dave

I think they said that to be more accurate the person being screened would have to be presented with lots of signals at different frequencies and levels all arranged randomly with unhearable sigs included at some of the test intervals.

I think that most audiologists use only a few frequencies and simply bring up the level until the subject indicates that they can hear the sig.

I mention this to possibly save folks the trouble and money of getting audiograms which may not necessarily be as accurate as most of us experimenters would like.

Guess I didn't copy over the stuff from the other thread. My main reason for chatting about CW was for high speed (qrq) op, at 60 to 100 wpm. 100 hertz bandwidth, of course, won't cut it there. Of course, CW and AM demod are different. The point I was trying to make was that there are similarities in the overall problem of hearing "something" and at the same time copying the message's meaning, i.e. content. Makes me wonder how many of us are/have built crystal sets wherein we've outbuilt or underbuilt relative to our hearing ability. A hearing floor, mentioned in RDRE is about 0.0002 dynes/cm2. I'm wondering where I stand to that average minimum signal (50% understanding of content)? Then likely overiding all of that is the cognitive aspects of the brain in processing di-dahs at higher speeds. Might be fun to "learn" a couple of hundred words at that speed. Hm?

Phil, WØXI

"One should never increase, beyond what is necessary,
the number of entities required to explain anything." What Would Maxwell Say [1831-1879]

The "ease" of listening and understandng the content is improved for anyone by getting the technical details right. It's especially important for me with my situation listening at passive set levels. I've gotten much background for this approach to improved intelligibility at low levels from my experience with '80s "High End" audio. This has driven my series of specialty intertests in this passive radio dicipline thru matching, headphone technicals, and onward to reciever design and details.
The result is a systems approach to my own sets that let me hear into a signal at very low levels and extract enuff content to understand the message. Concurrent is "sharpening" my hearing process, such as it is, to a point that is both amazing to me and gratifying. Nonetheless, I still must play the "sounds-like" game with station I-Ds and get corroborating frequency and locality data to make a positive 'hit' on a new station.
S.B.

There have been some studies that indicate loud speakers set apart from the listener at some feet AND within a small soundproof room do better than headphones in a soundproof environment. Also, little horns on piston transducers do better than standard headphone shapes; the piston does a better job of matching to the air.

Ironic! I was surfing the net couple of months ago and ran across a paper by an ME student in CA; he was modeling transducers. His advisor was a Dr. Ben Tongue. I emailed "our" Ben and he told me it was his son. Small world!

I may work up an experiment for CW in particular, looking first at optimal S/N and bandwidth required along with symbol optimization. Might be fun. Goal > 60 wpm, target 100 wpm.

Phil, WØXI

"One should never increase, beyond what is necessary,
the number of entities required to explain anything." What Would Maxwell Say [1831-1879]

Phil, WØXI

"One should never increase, beyond what is necessary,
the number of entities required to explain anything." What Would Maxwell Say [1831-1879]