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hey, do any of you know audio hardware stuff? i have a keyboard with a 6.35 mm (1⁄4 in) audio output. i believe it's stereo (trs). i want to record it without horrible usb interference noise, so i want something with uhhh some kind of isolation? (what is that called). what do i buy. i would prefer to spend less than 100 €
i probably want an “audio interface”, that's my going assumption so far, but something that is driving me up the wall is not even the good manufacturers seem to specify whether they can record in stereo. the fact the output is stereo means nothing, what about the input!!!
oh okay, the fact the input of the “scarlett solo” is mono is actually on their site at least (buried deep in the manual, not explicitly stated in the specification list)
oh my god why is every connector standard a compatibility nightmare. the way mono (ts) and stereo (trs) connectors interact is scary enough by itself, but then there's mono with differential pairs (“balanced audio”, also trs)…
from now on i am going to release my music recordings as 2-channel flac files, but instead of the second channel being intended for stereo, it's just the inverse of the first one. i'm calling it “balanced flac”
it won't be mid-side encoded because that would destroy the balanced property
the right audio channel isn't silent, it's just the mid channel of a mid-side-encoded differential pair,
huh, the “zoom ams-22” is a usb audio interface with stereo line-in. true stereo, not mixed down to mono. i think it's the first one like that i've found! it's also like, tiny. weird, fascinating product
hey wait! i have a computer!!! you know, like a computer computer, a big box with a motherboard in it. remember when people bought those?? well, it has integrated sound i/o, like any computer sold this century. and like many such computers, it has three audio jacks: line out, microphone in, and… that's right, stereo line in!!! and wouldn't you know it, the recording quality is fine and doesn't have horrible USB noise. thank god, i've just saved myself so much hassle and expense.
the things we lose in the transition to laptops and smartphones, huh? with a laptop, you're lucky to have even a single audio input channel, whereas your average PC has three!
many pc motherboards have eight audio output channels too (7.1 surround). i think mine does as well, but it's one of those more compact models with just 3 ports rather than 6, so i would need to do some driver shenanigans to switch the functions of the ports (yes that's a thing)
haha omg it even has 192kHz, 24-bit recording
there's no way the noise floor is low enough on this thing that 24-bit is worth it, but hey this is still way better than your average usb audio device can do :3
anyway here's a song from the yamaha psr-350 recorded via my pc's stereo line-in. https://hikari.noyu.me/etc/2023-07-30-psr-350-song-009-Sometime.flac
(does the fact i didn't try to filter out the noise mean you can steal my encryption keys now? lol)
what did we learn from this? pc users stay winning and usb delenda est, but we knew that already
omg… since i have line-in monitoring turned on, and my keyboard is turned on and connected to my pc via both line-in and my usb midi interface, i can just use it as my normal midi synth for everything. like, i can hear its output and normal sound from my computer. this is the 1990's pc midi dream
ah goddamnit that introduces noise from the usb midi interface
ok so, having my usb midi interface connected seems to unavoidably create an audible (circa -32dB) hum when recording my keyboard's audio output. is this the kind of thing that's avoided if i get an audio interface with a built-in midi interface? the midi interface i have might just be bad though
@hikari is it 1kHz or 50/60Hz or something else
@rcombs here's a spectrogram if that helps
@rcombs left is before connecting the midi interface, right is after
@hikari oh, so it was always there, but connecting the interface made it louder? hmmmmmmm
okay maybe this is something something rectified european AC (thus 100 instead of 50)? maybe off a crappy power supply?
and maybe connecting the external device is creating a ground loop and exacerbating the existing problem?
@rcombs yeah probably. i suspect the usb buss power from my pc is quite noisy and i doubt this cheap usb midi interface is properly isolated. also, the keyboard has its own psu which might not be good either. i generally am very suspicious of the quality of my ac power lol
@hikari huh, so somewhere around 100Hz, with a whole lot of harmonics? that's… unexpected, not sure what the source would be :/
@rcombs well, considering there's at least two power supplies involved here, there's plenty of possible sources of noise
@hikari do you have things plugged into separate outlets? how much stuff here has ground connections? is there a MIDI cable involved that had continuity from shield to shield?
@rcombs uhh, the pc is connected to the same power strip as the keyboard's power brick, but only the pc is earthed. the midi interface is a unit with three fixed/integrated cables: one usb (power and i/o) and two midi
