An unexpected measurement

[RayDunzl]

Fooling around...

This shows the spectrum of the harmonic series of a 10Hz Square wave here at Neverland East, out to the umpteenth odd harmonic.

(click and double-click to expand the image)

The noise floor of my long cable from the preamp to the the PC is the dark stuff at the bottom.

I never expected to see this many frequencies in the series, I figured they would disappear much sooner.

This goes to about the 1,150th odd harmonic of 10Hz.

Bleh.

 

[FrantzM]

Ray

What is surprising? That the measurements show so many harmonics? I would expect it to since we are dealing with only 10 Hz fundamental. A square wave is made of an infinity of odd harmonics regardless of frequency.

 

[RayDunzl]

I expected the series to disappear into the noise floor.

It didn't, so I had to think about it a little.

With a -25dBfs signal, the 1,150th odd harmonic would be 1/1150th of that signal voltage, which would be about 61.2dB down, and not dropping very quickly as the series progresses.

For my case, 96 -25 -61 = 10 which isn't too far off from what displayed.

So, it makes sense, but it sure caught my eye initially.

 

[Blumlein 88]

Sawtooth waves are pretty too. They have even and odd harmonics.

 

[RayDunzl]

Sawtooth waves are pretty too. They have even and odd harmonics.

I learned (more) about waveforms when I tried to make "music" on my (then new) win98 PC. By that time they really didn't come with a 750 page manual that fully explained the workings of the sound hardware anymore, so I was (after looking at some actual Windows Spaghetticode) stumped at how to cause it to remake some tunes that I'd made on the old Commodore 64 with PEEK and POKE.

My elegant solution was to calculate what I wanted to hear sample by sample in nice utilitarian C code and write a WAV file directly, and not try to deal with the intricacies of the "sound" hardware or Windows Code at all.

Multiple voices, stereo, timbre, pitch, envelope, reverb, and it wasn't very many lines of code. Maybe a couple of hundred. All settings hardcoded, then let it run a ruleset to make a "song".

 

[TBone]

Multiple voices, stereo, timbre, pitch, envelope, reverb, and it wasn't very many lines of code. Maybe a couple of hundred. All settings hardcoded, then let it run a ruleset to make a "song".

nice ... Lindsey Buckingham did much the same when he made Tango In The Night.

 

[RayDunzl]

Sawtooth waves are pretty too. They have even and odd harmonics.

Check out the beauty of this recent preamp out RTA... (the spike is a leftover, ignore it)

Nice log sweep!

Ah, I can control the pattern:

Ok, we'll call this my second Unexpected Measurement.

 

[RayDunzl]

A square wave is made of an infinity of odd harmonics regardless of frequency.

"To a mathematician, infinity is simply a number without limit. To a physicist, it's a monstrosity... In the real world, there is no such thing as infinity." - Michio Kaku