Oscilloscopes - what specs to look for?

20 MHz is overkill for audio gear, unless you are going to start poking around in digital devices like a streamer or DAC.

You might want to look into some PC based solutions.  There's a number of capabilities the old school style oscilloscope may not have built in, which are useful:

• Spectral analysis
• Signal to Noise
• THD
• IM
  
• Jitter

Best,

E

my mentors Richard Vandersteen and Roger Modjeski ( rip ) both thought the Tektronix TDS-220 up to the task - i agree

What should I make sure I've got covered?

How about, to make sure you know what do you really need an oscilloscope for in the first place?

I mean, its not like you're just gonna be randomly messing around .. oh wait, what's this?

I'm going to use it to mainly fiddle

Okay well then maybe look for one with a fancy pretty screen and lots of cool knobs?

eyrepm, As Eric said 20MHz is an overkill for audio, but I would buy scope for any possible future adventure in electronics. The basic decision is how much you’re willing to pay. You can buy unknown brand for 30% of the established brand. What you’re looking for is around $200 for no name brand like one here:
https://www.amazon.com/Hantek-DSO5072P-Digital-Oscilloscope-Bandwidth/dp/B00RJPXB6Y/ref=sr_1_9?dchild=1&keywords=oscilloscope&qid=1586197467&sr=8-9
or 3x that for known brand like this one:
https://www.amazon.com/KEYSIGHT-EDUX1002A-InfiniiVision-Digital-Oscilloscope/dp/B06WXXBXKZ/ref=sr_1_2?dchild=1&keywords=oscilloscope+keysight&qid=1586197860&sr=8-2

Most of the scopes available now are sampling scopes, meaning they A/D signal. Benefit of that is memory function, while drawback is possible aliasing showing false results. I would go for 2 channel, 1Gs/s (most likely half of that when using both channels), 2mV per division vertical resolution and 5ns per division horizontal resolution. Many scopes have built in additional functions like Multimeter, FFT analyzer, Generator etc. I would go for Keysight and pay $600 because of quality, but Hantek might be OK. There are many things that can go wrong with the scope (mostly switches) so if you go with Hantek - investigate. Keysight used to be Agilent, that used to be Hewlet Packard (wonderful scopes). I used Agilent scopes at work.
On the other hand it is complicated instrument. Are you willing to learn? How much time you can invest? There are $50 toy scopes that might be adequate for basic functions in audio band.

Datasheet (just in case):
https://www.keysight.com/us/en/assets/7018-05520/data-sheets/5992-1965.pdf

My company has Keithley Multimeters that are about 50 years old and all of them work fine (are tested every year). That’s quality. On the other hand I won’t be living that long ;)

Let me know more about your needs/plans.

because ego is rarely a replacement for knowledge, I would also suggest an investment in Williams excellent text;; Analog Electronics - Devices, Circuits and Techniques a decent used copy can be had for $40 ish