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

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

#211

Post by raverbashing »

nickthegreek wrote: post #25

Just put a record on yesterday and my wife said it was playing too fast. I thought she was wrong, then I see this post today! I grabbed the app and gave it a go, 3.5% too fast according to your app. Now I have to figure out how to adjust the damn thing. Really appreciate a free nonsense free app. update: youtube to the rescue. pretty common affordable turntable( Audio-Technica LP60), so I figure I would put the vid l…

Curious. Does this turntable have the flashing lights that sync to the edge of the plate to indicate speed?

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

#212

Post by taylodl »

derefr wrote: post #105
egypturnash wrote: post #96

Earlier quoted context omitted.

My dad was a recording engineer, so he knew where to go to find the sweet spot between "this sounds great" and "this sounds insanely fabulous but requires a second mortgage". And yeah honestly I'm surprised you can get a turntable that isn't made for the audiophile market any more, but the one shown in the video for this app sure does lack any fine speed adjustment. Just a little button labeled 33/45.

> And yeah honestly I'm surprised you can get a turntable that isn't made for the audiophile market any more It's because of the other re-emerged market for vinyl: the "not-so-enthusiastic" collectors, who just want the album "on vinyl" to say they have the album "on vinyl" or maybe "in every possible format"; or because they love the band and the vinyl is just what you happen to get when you buy the special collecto…

Damn! I hadn't even considered that. You've opened my eyes to a world a never knew existed.

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

#213

Post by taylodl »

jimbobthrowawy wrote: post #190
taylodl wrote: post #83

Earlier quoted context omitted.

Correct. That was often done when mastering with tape. Record at one speed, playback at another to make it sound more "lively." There are songs that were sped up that way anywhere from 25 to 40 cents. It's another reason why live music so often doesn't sound like the recording. When using digital mastering, you can also adjust the playback speed, but you can correct the shift. You get more "liveliness" without the sh…

What are cents in the context of playback speed? Hundredths of an RPM?

There are 100 cents to a semitone - by definition. The frequency shift of a 25 to 40 cent adjustment isn't likely going to be noticed by the average listener. A lot of times you don't notice it until you try to play guitar along with the song and you notice something is a little "off."

In can drive you nuts when you're playing by ear because when trying to find the root note, i.e. the key, you'll find it between two semitones. Always go for the lower tone. For example, if it sounds like it's a little sharper than A, but it's definitely not Bb, then you know it was A and the mastering was sped up. That's another thing, in my experience it's always sped up and never slowed down.

I have a theory that one of the reasons Eb standard guitar tuning started becoming so popular in the late 60s and into the 70s was because the speed up was getting to be so common that guitar players started adjusting their tuning for it, not to mention you generally get a "heavier" sound.

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

#214

Post by chrisshroba »

kazinator wrote: post #192
jimbobthrowawy wrote: post #190

Earlier quoted context omitted.

What are cents in the context of playback speed? Hundredths of an RPM?

A cent is a factor of 2^(1/1200). There are 1200 cents in an octave, which is a doubling in frequency: if we have 1200 of them, 2^(1200/1200) = 2^1 = 2. Lisp-wise: 2> (exp2 (/ 1200)) ;; exp2 is courtesy of ISO C 99 1.00057778950655 So, it is a .0578 percent change in pitch, or determiner of pitch like record rotations speed.

A little more intuitively, 1 semitone is one "note", aka the interval between two successive notes on a piano (including white and black keys) such as C to C#, and to talk about intervals less than that, we use cents as 1/100 of a semitone.

Musically, two notes an octave apart vary by a factor of 2 (e.g. Middle A (A4) is 440Hz and the next A (A5) is 880Hz), and our ears hear frequencies logarithmically rather than linearly, so each of the 12 semitones in an octave is a factor of 2^(1/12) higher than the previous one (so that 12 of them in a row result in doubling the frequency), and therefore the 100 cents between each semitone are each (2^(1/12))^100 = 2^(1/1200) greater than the previous one.

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

#215

Post by taylodl »

criddell wrote: post #127
taylodl wrote: post #83

Earlier quoted context omitted.

Correct. That was often done when mastering with tape. Record at one speed, playback at another to make it sound more "lively." There are songs that were sped up that way anywhere from 25 to 40 cents. It's another reason why live music so often doesn't sound like the recording. When using digital mastering, you can also adjust the playback speed, but you can correct the shift. You get more "liveliness" without the sh…

Do you happen to know of any tools for fixing pitch issues in music files?

Depends on what you're trying to do. For guitar practice, I use AnyTune Pro+. I use for learning the lead, because with my musical experience I can nail the rhythm guitar part by ear in a couple minutes. Not so with lead guitar parts, I'm afraid! But yeah, you can adjust frequency, you can adjust playback speed, you can pick a point A and a point B and loop between those points (great for breaking down each section of the solo). If you slow the playback speed slower than 70% or so, you're going to start getting a lot of digital noise. Once you've learned how to hear the notes through the noise then you can learn even super fast solos.

As I'm writing this I'm thinking to myself I know there are AI tools now that can take any track and produce all the stems for all the different parts in the track. You'd think for something like the lead guitar they could analyze that stem and produce either the tablature or standard music notation for the solo. That would be kinda awesome! I wonder if such a tool now exists?

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

#216

Post by GuB-42 »

sambeau wrote: post #33
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…

My first thought was that it is listening to the scratches rather than the music, but I guess they speed up as the record gets played and the arm moves inwards. So, my second guess is that it's listening to the pitch of the notes being played. Of course, old albums (especially punk albums) are probably tuned to whatever worked on the day—maybe a tuning fork, possibly a piano, maybe just to one of the instruments.

As a turntable rotates at a constant RPM, scratches change in pitch (if there is such a thing) but it will always "pop" once per rotation.

My guess would be some filtering (to remove the actual music) and some kind of autocorrelation algorithm to detect some periodic patterns with a period matching the expected rotation speed of a record within a few percent (33.3 RPM, it doesn't talk about 45/78).

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

#217

Post by jerf »

crazygringo wrote: post #120
jerf wrote: post #117

Earlier quoted context omitted.

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…

I am 100% abundantly positive that signal processing code could do this, and in fact by signal processing standards it's not even particularly hard. You may need more time than the app takes, though I am inclined to think that the app doesn't exactly need a number to twelve significant digits and you could get a single-digit-percentage significant digit lock pretty quickly. Even at 33&1/3rd you only need a few seconds for three or four revolutions.

I am much less confident about my claims that it is something you could bash together in "normal code" from an FFT, without advanced math, but it still seems likely to me. You have huge stonking correlations between the frequencies you can exploit. Imagine a normal FFT chart like you've seen any number of times. Now, take that same thing and wave it up and down quite visibly on a sine wave. Nice and big in your imagination so you can see it. You think that's not something that could be picked up? Now, scaling it down to where you can't hear it anymore may make it harder to believe, but the same code will pick it up. To a computer it would still be clear as day. This is one of those things microphones pick up much, much better than human ears, just like microphones trivially pick up a quite 1001Hz tone next to a loud 1000Hz tone even though we can't hear it at all.

Compared to, say, recognizing a voice and extracting words from it, this is pretty trivial stuff.

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

#218

Post by sgarland »

bitnasty wrote: post #208
jiayo wrote: post #150

Earlier quoted context omitted.

When US (NTSC) shows are aired in Europe (PAL), the framerate difference necessitates a small speed-up. It's barely noticeable, except when music is playing, at which point it is very, very noticeable. Yes, it's a little higher pitched, but it just feels wrong and is immediately noticeable. I think it's about 3% speed up, which is exactly what's being described here.

NTSC is 29.97 fps and PAL is 25. That’s almost 20%!

They may have been referring to film (24 FPS) or its broadcast equivalent (23.976 FPS) being shifted to PAL, which is quite a bit smaller of a jump.

NTSC —> PAL can either be annoying, or difficult to manage without artifacts. If the NTSC source is telecined from a 23.976 source, you can invert that process to get the original back, and then deal with the minor time shift to PAL. If it’s pure NTSC, there’s a lot of filtering to be done to get an acceptable result. At least, last I played with it.

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

#219

Post by davidmurdoch »

okatbest wrote: post #164
opello wrote: post #161

Earlier quoted context omitted.

This is pretty cool, thanks for sharing it. Is this the aforementioned comment about _why_ you aren't being specific about the implementation? > Eventually I decided to see if I could find a novel, more user-friendly approach that doesn't require you to put a thousand-dollars phone on a fast moving spinning thingie, and that's how Grooved came to be. If it isn't then I couldn't find it. I was very curious about that…

Here's the comment: https://news.ycombinator.com/item?id=40502383 Essentially I don't want to have somebody swoop in, replicate the same thing, be better at marketing, and charge money for it. I'm both protecting users because they shouldn't be charged for something that is free, but also protecting my ego because I spent time and effort and as far as I can tell I'm the first one to build an app that works this way a…

Usually when an app comes out on iPhone but not Android the excuse is that "Android users don't pay for apps so it wasn't a priority", despite it being way more difficult and a bit more expensive to develop for iPhone over Android.

But in your case you don't plan on monetizing, so why iPhone first?

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