and a USB analyzer costs under $10 on eBay (or more than $10 if you want an even better one) - much cheaper than the hundreds of $$ a logic upgrade to an oscilloscope costs.
USB "analyzer" (what analyzer) is not oscilloscope at all. How you analyze signal waveform with these kind of USB "analyzers". They show only decode result or just binary state from signal but you do not see this signal itself at all. Oh you can use external scope for this but where is then time synchronization between scope screen signal and computer screen decode result or 1-0 states.
MSO is just for look digital AND analog signal together with tight time synchronization if use digital channels for decode some serial communication or some other bus. If do not use digital inputs for decode then use analog channels for decode and you have decode and decoded signals analog waveform between signals with tight time synchronization on the screen.
Cheap USB "box" can not do this at all. If only need decode, both scopes have free serial decoder and in this Siglent have bit more than this Rigol.
But then, if need MSO functions what means integrated scope and LA then these cheap USB decoders are not these at all)
So if example later user find that he need MSO with 4 analog channels and 16 digital channels what can use all fully together simultaneously he do not need buy new scope if he have SDS1104X-E.
But if he have DS1054Z or 1104Z then this is just impossible. Only way is buy whole new MSO scope and there come Rigol MSO1104Z. But again, it is mostly same as DS1000Z models with all its goods and bads.
Example fact that it can not do
simultaneously 16 digital + 4 analog. You need drop off more or less analog channels if you use digital channels. If want 16 digital then only 2 analog channels can use. Siglent is different. Fun - is it.
This is fun to say that Siglent need buy expensive extra options... if user need options yes, but then also compare to other brands need do fair way. Even if you buy R. MSO1104Z (in europe consumer price typically 950 eur) do not get even nearly same as with SDS1104X-E + MSO-LA option what european consumer price is around 965 euro).
Some ask why Siglent MSO-LA option cost hundreds.
But when we go to Rigol, why not ask why MSO model price is hundreds more than same without MSO. Fun - is it.
Oh well, and then some may tell that 50MHz Rigol can hack to 100MHz model. Well, at this time yes.
But, at same time Siglent 100MHz model can hack afaik 200MHz model. So
And prices. 40% cheaper?? Yes it depends...
Consumer prices, well known very reputable and trusted "spitzenklasse" Batronix:
DS1054Z. 403 eur
Siglent SDS1104X-E. 510 eur.
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But then. All what is important is what meets user needs!
And here, imho, even DS1054Z is more than OP need if need is all what we can see here.
For
audioit is true that many sound cards and PC software can do lot of better work than 8 bit ADC oscilloscope with what ever memory length. Even normal "crap" sound card what every computer have (more or less crap) can do better, and if want or need better or lot of better then need - money or lot of more money.
I recommend first test with just this sound card what is in home already and some free software and if never have seen what these can do without any investment - it may be astonishing.