On 12/22/2015 8:53 AM, Tim R wrote:
On Tuesday, December 22, 2015 at 11:39:49 AM UTC-5, Phil Hobbs wrote:
On 12/22/2015 11:02 AM, c4urs11 wrote:
On Tue, 22 Dec 2015 05:59:52 -0800, Tim R wrote:

However, my question is about how you would use a 1950s era scope
to determine a sine wave or the degree of harmonics present.

Scopes from that era easily reached several MHz of bandwidth.
That should be considered adequate to inspect audio signals.

Cheers!


The eyeball is a really lousy detector of harmonics, though, especially
odd harmonics.

Plus he had to use a 1950s-era microphone, so the scope bandwidth is
irrelevant.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

I've used an RTA, but those hadn't been invented yet. Before my time, but wasn't there something called octave filters?

The experimenter wasn't real detailed but supposedly he could tell from looking at the scope that it was a pure sine without harmonics. I was very skeptical that 1950s technology allowed that. He is a believer that the material a trumpet is made from determines the sound, whereas many of us believe it is the shape of the air column.

I will quote the article:
******
At one time we ran an experiment in which we used steel, aluminum, various plastics, glass, silver, various combinations of brass and the last one we used was lead. To demonstrate results as quickly as possible, I will choose the two extremes. The steel bell, which we tempered so it was extremely hard, gave possibly one of the most interesting results. Many people test a bell by tapping it with their finger or knuckle and in tapping the steel bell, it would emit a very ringing sound, truly like a bell. However, when we played this instrument, the quality of sound was extremely dead. On searching for the reason for this, we looked at the oscilloscope when the performer played on the instrument and found the sine pattern very faint but the distortion pattern, coming from the vibration of the bell itself, going through at a very jagged and rapid rate, killing the brilliance of sound of the true tone. At the other extreme was the lead bell. This bell, if rapped with your knuckle, emit
ted an extremely dead sound like rapping on a piece of wood. However the sound that emanated when it was blown was extremely brilliant, brilliant to the point of being mechanical. This showed up on the oscilloscope as a perfectly true sine pattern, there being no distortions in the harmonics either above or below, and, as a result, the sound was absolutely pure but not usable musically, except for a general effect such as a percussion instrument would give. The voice, you know, registering on an oscilloscope, gives harmonics both above and below the note. These distortions, if we may call them such, give warmth to the tone. We have to have that "distortion" in order to have the sound acceptable to our ears as a musical sound.


Could you give a citation, reference (or even a URL) to the article.
I'd love to read it.
Thanks