In article ,
Phil Hobbs wrote:

On 12/22/2015 11:53 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.


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.

Well, he was wrong about that. Even 10% third harmonic isn't easy to
spot unless you have a comparison sine wave on the screen at the same
time. (I'm thinking about zero degrees relative phase, so the peaks are
symmetrical. It's a bit easier to see at other phases.)

I was very skeptical that 1950s technology allowed that.

Unless he had a really expensive ribbon mic, his 1950s microphone had a
heavy diaphragm and rolled off really badly above about 5 kHz. (One of
the audio guys will correct this, but it's roughly right.)

Condenser mics were not common at that time, but certainly were not
rare, either. The Altec 21B went to 15 kHz, which would handle the
overtones of any real-world musical instrument easily.

Isaac