A fellow DIYer in the digital audio community was concerned that I was measuring 5-50Mhz osc (clocks) w/o the use of a 50-ohm adapter.
I didn't know I needed one at those "low" freqs -- and especially given my traces and wires are very short in length (nothing over 0.1meter) .
Both my Siglent SDS-1202X-E and Tek 465 have the typical 1M-ohm input.
Why might I need a 50-ohm adapter for digital audio design?

 

You don't need a 50 ohm input for those frequencies, but a 10:1 probe that you have properly compensated is definitely needed.
I don't consider 5-50MHz a "low" frequency when it comes to proper termination.
A standard 50 ohm coax cable connected to the 1 meg scope input will likely cause significant distortion and ringing of the signal at those frequencies.

You typically shouldn't go above audio frequencies without using a 10:1 probe (or 50Ω coax with a 50Ω termination).

 

A fellow DIYer in the digital audio community was concerned that I was measuring 5-50Mhz osc (clocks) w/o the use of a 50-ohm adapter.
I didn't know I needed one at those "low" freqs -- and especially given my traces and wires are very short in length (nothing over 0.1meter) .
Both my Siglent SDS-1202X-E and Tek 465 have the typical 1M-ohm input.
Why might I need a 50-ohm adapter for digital audio design?

These are two separate issues.
Oscilloscopes typically have 1MΩ across 20pF inputs. You should use the 10x attenuation probe that is supplied with your oscilloscope. This will increase the input impedance to 10MΩ and will extend the usable bandwidth of the oscilloscope. This will minimize loading on the signal source.

If you intend to view HF signals with RG-58/U coaxial cable, then you should use a 50Ω terminator at the input of the oscilloscope. This will minimize reflections in the cable.

 

A fellow DIYer in the digital audio community was concerned that I was measuring 5-50Mhz osc (clocks) w/o the use of a 50-ohm adapter.
I didn't know I needed one at those "low" freqs -- and especially given my traces and wires are very short in length (nothing over 0.1meter) .
Both my Siglent SDS-1202X-E and Tek 465 have the typical 1M-ohm input.
Why might I need a 50-ohm adapter for digital audio design?

What do your signals look like? Post an image if you can. 0.1meter, at 50MHz, is getting close to having sufficient energy in the transmission line space from point A to B to need proper source drivers, cables and termination if you care about scope signal display fidelity. It's unlikely to affect any synchronous audio signal physical layer that uses or generates clocks from digital signal edges.

https://forum.allaboutcircuits.com/...onfigured-as-an-spi-slave.192845/post-1811466
SPI signals at 30Mhz on a 5 foot loop of wire measured with a 10x scope probe. It looks messy (as expected) but works perfectly.

 

Why might I need a 50-ohm adapter for digital audio design?

I may have missed the point about "digital audio design".
We know that customarily, audio frequency range is 20-20kHz. You would not need special cable termination at these frequencies.
The "digital" part means that clock and data bandwidth would be far in excess of 50MHz clock frequencies.
If you are just 'scoping digital signals, continue to use the 10x attenuation probe on your 200MHz bandwidth oscilloscope.
If you are routing digital signals from one point to another, then that is totally different issue.

 

The topic of this thread orig. arose here:
https://pinkfishmedia.net/forum/threads/got-ticks-and-fleas.280281/page-2#post-5028581
Maybe you can figure out what Martin is getting at .... because I sure can't!

 

I may have missed the point about "digital audio design".
We know that customarily, audio frequency range is 20-20kHz. You would not need special cable termination at these frequencies.
The "digital" part means that clock and data bandwidth would be far in excess of 50MHz clock frequencies.

The max osc freq. I've seen in digital audio is 80Mhz, but 45mhz is where many of the high rangers reside. Typically, I see 11.289 to 27Mhz. The latter in certain DVD players.

 

If you are viewing a 50MHz digital signal, you need a viewing bandwidth of at least 5 times that, i.e. an oscilloscope of 250MHz bandwidth.

 

The topic of this thread orig. arose here:
https://pinkfishmedia.net/forum/threads/got-ticks-and-fleas.280281/page-2#post-5028581
Maybe you can figure out what Martin is getting at .... because I sure can't!

That link is into the magical kingdom of audio. It's a place where factors that don't matter in high speed RF digital signals suddenly can be heard (like ps RMS clock jitter) by 'Golden Ears'.

IMO, just move on.

 

I wonder if he expects to improve upon a distortion-level that is
proven to be way beyond the capabilities of Human-Hearing ?

Oxygen-Free-AC-Power-Cords anyone ?
.
.
.

 

The max osc freq. I've seen in digital audio is 80Mhz, but 45mhz is where many of the high rangers reside. Typically, I see 11.289 to 27Mhz. The latter in certain DVD players.

Good luck with signal integrity if you have any of those high frequencies running around in the rat's nest of wires you posted.