whats the best way to measure delay times on a scope of bbd?

[njkmonty]

playing around with mn3007/ mn3207 chips  and clock frequencies, wondering whats the best way to use a scope to compare input and output signals to measure what actual delay time a bbd is
doing?
use a particular waveform?

[anotherjim]

I don't like using 'scopes for relatively long time measurements. I'd record into software - original to left, delay to right. In a decent wave editor or DAW you should be able to measure cursor or selection times in seconds & milliseconds.
I think I would really trust a chip to have it's specified number of stages and instead measure the clock period and calculate the delay.
For a test input signal, a single impulse click is best, but any signal will do for the recording method. In a DAW, the test signal can be on another track but still record 2 tracks from it since you don't want the play & record buffer latency of the audio interface to affect the time measure.

[ElectricDruid]

I agree with Jim that a simple way is to instead measure the BBD clock and calculate the delay time.

That said, when I've done what you suggest, I've got reasonable results by setting up a synth to produce regular repeating "ping!" noises (a brief sound with zero attack and short decay/release, triggered by an LFO - like a metronome). This gives something obvious on the scope so you can see the difference between the input and output. My scope is dual trace, so I can see input on one and output on the other. This is fine to give an idea of whether the BBD is working, and what sort of delay range you get when you twist the clock frequency pot and so on.

What's the motivation for this test?

[njkmonty]

i have a newish siglent dual channel scope, (still exploring its features& learning how to use )
I was looking at different bbds (of different delay stages eg mn3001/mn3007/mn3008/ mn3009)
and was trying to get an accurate delay figure to see if i use a different bbd chip  with adjusting clock frequency
could measure the delay time in order to replicate it in a different chip
when i was viewing the input and output of the bbd, I was finding it challenging .
I wasnt sure if i needed to use a pulse signal or something else, or some different setup in order to view the difference.
Does this make sense?
I thought it would be easy to do,  I have no probs viewing clock signals etc , but thought there may be a trick that those more knowledgable would know

[Scruffie]

As has been said, what you're trying to do is easily calculable.

# of stages, divided by 2 x clock frequency.

There shouldn't be any reason to actually measure it in the way you describe unless you suspect the chip is fake.

[njkmonty]

I appreciate all responses, I guess having a new scope and exploring its features,
I was hoping to be able to see it on a scope.
i had a play around with different bbds and adjusted clock frequencies on the chips with more delay stages
i found the delay sounded close , but i thought if i could actually measure it,
i could tweak to get it closer?

[Rob Strand]

i could tweak to get it closer?

Do mean you want to match the delay?

As far as a fixed delay goes you cannot do better than measuring the clock frequency, as everyone has mentioned.
So are you measuring frequency as good as you can on the oscilloscope.  Like you can eye-ball one cycle on the display and used the graticule, better is to measure many cycles and use the graticule.   Then there's measurements which are displayed by the oscilloscope, assuming you have that feature.   Some use cursors, some have direct  period or frequency measurement; which can depend on set-up and number of cycles displayed.  The uS/div on Analog oscilloscopes can be off if the oscilloscope isn't calibrated;  but that doesn't affect matching.

One of the best ways to measure frequency is a frequency counter.   Some DMMs have them but many aren't they accurate as they use analog methods or have poor trigger algorithms.

As far as seeing delay on the CRO display, simple methods are to use narrow rectangular pulses, square-waves, or even the zero crossing of sine-waves.  They all have their problems and you should keep in mind that the filters before and after the BBD can skew the waveforms and give a perceived delay.

When you have a delay which is modulated like on a chorus that brings up a whole heap of other problems since you are trying to measure a moving target.

[Scruffie]

There's also the fact that BBD's each respond differently at different clock frequencies regarding gain, high cut etc. the datasheets will help with this to some extent. Could be why what you're hearing isn't what you think you should be hearing?

[njkmonty]

ive got the full panasonic pdf spread out in front, and ive discovered the different effects of the high end as mentioned,
I was just unsure if everyone went about it completely different and i was doing the wrong thing!
ive matched two bbds fine now but strangely the longer delay chip has more highs ?
its db is slightly higher too,
Im stumbling around but finding this very interesting

[Rob Strand]

ive matched two bbds fine now but strangely the longer delay chip has more highs ?
its db is slightly higher too,
Im stumbling around but finding this very interesting

You can match dB by measuring the level (say using the CRO) but it should be away from the filter frequencies.

As for high-end difference the filters can have a large effect.   Tolerance in the parts can easily cause 1dB difference at frequencies near the filter cut-off.   You would need to separate out the filters and measure the filter frequency response at a few frequency points.

What you can do is test at a fixed frequency and vary the clock and see what happens to the level.  That should show up BBD effects.

[Fender3D]

use a particular waveform?

You'll need a burst wave, the same use to check amplifiers...
Inject a burst of any sine or triangle or square waves and check for the burst at the output.

[PRR]

> strangely the longer delay chip has more highs ? its db is slightly higher too,

The very first BBD were short and awful. As the technology improved they gained fidelity which allowed longer lengths to be practical.

Your car has more speed and space than the first Benz or Ford. Even compared to the fine cars of 1940, today's cars do many things better. BBDs have the same historical trend.