Dear regulars and pros,
I am a beginner and this is my very first post. I have some questions but I probably will confuse things and especially the technical terms, so bear with me.
I am an analog synthesizer enthusiast and in order to learn more about analog sound synthesis, I want to monitor audio signals to both hear and see them to understand them better. In order to "stay true" to the analog world, I bought an analog oscilloscope, the Grundig GO 15Z. It is a 15 Mhz twin-channel, technical details can be found here: http://www.radiomuseum.org/forumdata/upload/d_Grundig_GO15-Z_man.pdf. It was quite cheap but it is working quite well as far as I can tell. As with all analogue equipment, I like how it displays the signals, without those digital pixel "staircases". In order to monitor the audio signals of an Arturia Microbrute analog synthesizer, I hook up the Grundig to the Microbrute's headphones output using a BNC-to-3.5mm adapter cable. When playing back a note in the upper register on the Microbrute, I adjust Grundig's time base switch accordingly; this switch is labelled "s/cm", the values range from 0.1s/cm to 0.3 microseconds/cm.
When, for example, I play the highest C, I adjust the switch to 0.1m and I can see very clearly the waveform, with several wavelengths on the Grundig's screen displayed. Usually, I like to display two, three or four wavelengths, to get a clear overview of the audio signal.
""Wavelength" is the wrong terminology----what you are referring to are "cycles".
The duration of each cycle is that time it takes between a point on a waveform,& the equivalent point on the next cycle.This is normally expressed as between the first ,& third zero crossings of a sinewave.
A "wavelength" is the distance a signal will travel in a given time.
For Electromagnetic waves this is specified as in free space,but in air the differece is negligible.
Acoustic waves are different,with the wavelength varying with the media-it is different in air,compared to water,for instance
The signal is displayed very sharply and the picture is very stable, so that I can "study" unhurriedly the different effects of applying the cutoff, resonance or pulse width to the audio signal using the Miscrobrute's knobs. So far so good.
When playing lower notes, the audio frequency goes down, naturally. Thus, to get a proper view of the signal, I have to adjust the time switch accordingly, of course. When playing the lowest C on the Microbrute, I have to set the switch to 3m or 10m to see at least one or three wavelengths,cycles accordingly.
I assume this is C1 of the equal tempered scale,which is 32.70Hz.
But when dialing these values, the horizontal sweep becomes visible.
This is a very strange comment,as the horizontal scan is always visible---that is what you look at!
Is it possible that you have the 'scope set to "alternate sweep,& are seeing the other channel?
In AC coupled mode,this may appear in line with the centre line of your display.
"Alternate" will present one channel's output at a time,& will cause quite a lot of flicker"---that is why "chop" is used to display both channels at low frequency settings.
When the time base switch is set from 0.3m to 1m, the picture starts to flicker slightly but visibly; but when switched to 3m, the picture flickers very heavily and strains my eyes.
At 1ms/div there should not be any visible flicker,& at 3ms/div,flicker should be barely discernible.
When switched to 10m, you can clearly see how the signal is quickly drawn from left to right.
Taken literally,this should not be evident until very much slower speeds are used.
This leads to a very unstable picture and it is very wearisome to look at the Grundig's screen and work with the audio signal. What I actually want to achieve is a stable picture without much (or ideally without any) flickering, regardless of the audio oscillator frequency or magnification on the oscilloscope; i.e. regardless of how high or low the note is and how many wavelengths cycles.
Now, my questions are: is the aforementioned flickering a normal behaviour of all analog oscilloscopes,
Yes,but not to anything near the extent you are experiencing.
or is it just a shortcoming of my particular model?
Perhaps,or as suggested above,it may be an artefact of how you are using it.
Also, a general question: What is your experience with visualising audio signals with analog oscilloscopes?
Greetings from Germany
MAB
Analog Oscilloscopes were,& are, used widely to look at low audio frequencies,as well as others using the same time/div ranges.
In Analog TV,it was common to look at 2 fields of the video signal,requiring for 625 line systems,a total of 40ms scan time..
With most 'scopes the most convenient setting is 5ms/div,with a total scan time of 50ms.
I have done this many times without experiencing any discomfort due to flickering.
So as to not rely upon memory,I set up the following test gear:
Tektronix 7613 Oscilloscope with 7A18 vert & 7B53A horizontal plugins.
As the 7613 is a storage 'scope (although I would only be using it in "non-storage" mode),I also included a
Jaycar/Digitech 10MHz single channel 'scope to "keep the Tek honest".
Signals were supplied by a Levell TG200D RC Oscillator & its frequency verified using a
Victor VC3651 counter.
Testing the 7613 with a 32.70 Hz signal, at 2ms/div,5ms/div,& 10ms/div, a stable display was obtained ,with perhaps a small
amount of flicker (it looked more like amplitude "jitter")
Stable triggering was obtained at frequencies down to the point where the display was just a moving dot.
At no time was the display objectionable enough to hurt my eyes.
The test was repeated with the Digitech with similar results.