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Show HN: I made a free app to calibrate your turntable by simply playing a song

grooved.okat.best

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Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#111

Post by okatbest »

crazygringo wrote: post #26

This seems really clever -- kudos! I'm curious how it actually works? At first I assumed you were comparing the vinyl track to the reference digital track from some streaming service and either analyzing the frequencies with FFT or the timing of peaks. But I watched your demo video and you don't need to tell it anything about the song. Which makes me think you're rather doing an FFT and simply trying to match how wel…

Thank you so much! I spoke about why I'm not flat out saying how it works in another comment but let me answer your questions:

1) It actually might! Worth a shot I guess, but I don't have any comedy albums to try it out. I was able to get drum solos working fine

2) Was answered better by somebody else

3) I was able to get it to detect speed issues up to 9% off, beyond that it just stops working completely. Though that was in controlled environment so YMMV. If you see the sample vid I posted above, my player is roughly 4% off which is a lot but I genuinely believe a whole lot of people wouldn't notice that

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#112

Post by pimlottc »

astral303 wrote: post #23
patrakov wrote: post #5

Does it rely on the fact that music has a concept of notes with well-defined frequencies and that there is no such thing as 216 Hz (must be 207.6 or 220 Hz) when the music is played on a properly tuned instrument? Or does it use other heuristics?

I tried it out and the instructions have tips on what record to pick, they say to pick a well known version of a song (like not a live version etc), and preferably song with a beat, but it says it doesn’t use any 3rd party APIs or libraries, only Apple APIs. So my guess at to what it’s doing is using a ShazamKit recognition behind the scenes and looking at the frequencySkew value of the matched result. It also gives…

I love that everyone is guessing all these methods of detecting pitches or using the camera to count rotations, and it turns out that they're most likely literally just using a built-in API and displaying a return value [0].

0: https://developer.apple.com/documentation/shazamkit/shmatche...

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#113

Post by chriscjcj »

So is this just a test to see if it's playing records at the right speed? Does it do anything else? Is it comparing it to a known-good recording of the song or is it measuring how many cents the song deviates from a natural key? If it's the latter, I can say that I have many many records don't play back in a natural key.

I have several records (45's) in my collection whose hole is not punched perfectly in the center and the pitch wavers up and down as the record rotates. How would this app react to that and what suggestion might it make to mitigate?

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#114

Post by pimlottc »

stavros wrote: post #69
padenot wrote: post #44

Earlier quoted context omitted.

ShazamKit, from that fetch the BPM, BPM detection from the mic, compare ?

It works offline, though.

Does it? I don't see that claim being made anywhere.

They do say that the audio is processed locally, but that does not preclude them from making an API call to find a signature match.

> The audio stream is processed locally on your device and never recorded.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#115

Post by okatbest »

dmd wrote: post #100
okatbest wrote: post #98

Earlier quoted context omitted.

That's odd, could you share an example of a record you use? Are those fairly popular/common records? Also, do you see the little disk outline moving during the analysis? This would confirm that your phone can hear the sound coming out of your record player (just to be safe: you need to play the song out loud)

I've tried the White Album, Tiffany (I think we're alone now), and a bunch of songs on Cake Comfort Eagle. No, the disk is not moving at all! It's turned up pretty loud.

That's super odd. So it's not even rotating? There might be an issue that occurs before the analysis starts.

If you don't mind, do you have any special setting on? Lockdown mode or something? Are you able to play the music back if you use the Voice Memo app to record a bit of it?

Sorry about all that, hopefully we can figure out what's wrong!

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#116

Post by okatbest »

kazinator wrote: post #43

I'm skeptical; you have no idea whether a random song from a record player is in tune or not, without a reference copy of that song from digital media. Is this zeroing in on traces of 60 cycle hum in the recording? Or else, won't it adjust an out-of-tune song to be in concert pitch? (Mind you, that would be extremely useful if you're playing along with the track and don't want to adjust your instrument, or cannot do…

Unfortunately a lot of mid-range tables nowadays don't have the strobe (mine included), most likely for aesthetic reasons... Even just looking at online shopping right now I only see a handful that do have it.

As for being skeptical, good! That means I'm doing something great according to Clarke's third law.

You can see me testing out the app on multiple records here: https://twitter.com/OKatBest/status/1795453042994680148

The results aren't 100% perfect, and they definitely won't be as good as matching specific frequencies, but it'll get you very close to the ideal RPM.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#117

Post by jerf »

mlyle wrote: post #104
jerf wrote: post #91

Earlier quoted context omitted.

I would expect: 1. Detect wow: https://www.youtube.com/watch?v=kCwRdrFtJuE 2. Time wow. 3. Round to nearest record speed and report delta. I'd also expect that armed with a normal FFT algorithm that Ye Olde Bash On Algorithme Until Functionale would be fairly likely to work with reasonable effort, without having to get too "signal processor-y" on the FFT output.

Wow is wavering speed. A constant turntable speed error (that this helps you calibrate out) doesn't produce wow.

All turntables have wow. Wow is determined by the rotational speed. So if you measure 33.2326 wow oscillations per minute, you can know the turn table is a touch too fast. Wow would not be used to measure the error, it would be used to measure the absolute speed. Getting the error from that point is trivial.

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#118

Post by dmd »

okatbest wrote: post #115
dmd wrote: post #100

Earlier quoted context omitted.

I've tried the White Album, Tiffany (I think we're alone now), and a bunch of songs on Cake Comfort Eagle. No, the disk is not moving at all! It's turned up pretty loud.

That's super odd. So it's not even rotating? There might be an issue that occurs before the analysis starts. If you don't mind, do you have any special setting on? Lockdown mode or something? Are you able to play the music back if you use the Voice Memo app to record a bit of it? Sorry about all that, hopefully we can figure out what's wrong!

Yep, voice memo works fine, not on lockdown (not sure what that is).

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#119

Post by verelo »

So this is super cool but i am questioning its reliability after playing a song from Spotify on my Sonos and then letting the app listen: the result was 0.1% too slow? I guess that’s a very small difference, what’s the degree of error to expect here?

Re: Show HN: I made a free app to calibrate your turntable by simply playing a song

#120

Post by crazygringo »

jerf wrote: post #117
mlyle wrote: post #104

Earlier quoted context omitted.

Wow is wavering speed. A constant turntable speed error (that this helps you calibrate out) doesn't produce wow.

All turntables have wow. Wow is determined by the rotational speed. So if you measure 33.2326 wow oscillations per minute, you can know the turn table is a touch too fast. Wow would not be used to measure the error, it would be used to measure the absolute speed. Getting the error from that point is trivial.

I don't think you could use FFT or similar to reliably measure wow to anywhere near the accuracy necessary to produce a reliable amount of correction from just a few seconds of an arbitrary LP.

If you were using an LP with a known pure 440 hZ sine wave that you could lock onto exactly, then sure. That's kind of how frequency modulation -- FM radio -- works.

But I really don't see how you could do this with songs that are full of frequencies coming in and out and changing all over the place. If you analyzed the full side of the LP, you could probably get enough signal out of that.

But trying to measure the precise wavelength of wow when you're only getting a few wavelengths' worth, from a complex signal? I don't see how.

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