On Mon, Oct 07, 2002 at 05:34:59 +0200, CK wrote: Presumably getting the dubplates cut is the hard part? Did you find somewhere to do it for a reasonable price? - Steve

On Mon, Oct 07, 2002 at 05:34:59PM +0200, CK wrote: Great! How does it present the position/rate data? Is there any standard protocol which could be used for this information? It would be neat if the whole setup could be wrapped as a userspace device, which apps can program against. I can think of at least two open source digital dj apps which could benefit (gdam and terminatorx) How do you handle lifting, moving, and setting down the needle? Could we get needle-up and needle-down events? Using an actual turntable for a physical interface has benefits and drawbacks. Many people have experience with real turntables, so it makes the switch to digital very natural. Turntables are also a very popular image in pop culture. Records pack a lot of information into a small space, with very quick access to small (along the groove) and large (across the groove) position changes. But at the same time, there are drawbacks to turntables.... they are expensive, large, heavy, need to be positioned on a level surface, susceptible to skipping from bumps dust and scratches, pick up noise from tapping on the body or bass vibrations. I imagine that a simple sawtooth pattern is easy to pick up through a fair amount of noise, and some skips could be filtered out by a bit of logic which analyzes the output position... nevertheless, scraping diamond on plastic seems crude. I'm looking forward to a lightweight, portable, digital turntable-style interface which outputs MIDI or some other open protocol. Similar to the new pioneer cd decks, but without the cd player and audio hardware, and with MIDI. The pioneer has quite good tactile response. However, there are a few scratches and techniques which rely on the fact that the turntable platter is actually spinning and the record is moving relative to it... until someone makes an interface with a spinning platter (or at least a scheme to make up for it, so these techniques are possible and natural) some dj's will only use real turntables for an interface. For real turntable interfaces, options include reconstructing position from an audio signal, or an optical solution (die-cut, printed, stamped or stickered record with optical detectors / optical mouse shining on them) The dubplate / reconstructed audio approach has the benefit that turntables can be used without any modification, or mounting extra hardware. -geoff

we Well i guess encoding absolute time should not be too hard. A simple solution could be to have the two stereo channels with different frequencies, with the ratio corresponding to the radial position. Or is that not accurate enough? How fine-grained is the time resolution of the final-scratch system? Rising slope, i guess. greetings, T

On Mon, 7 Oct 2002, Steve Harris wrote: records include stereo information by having different sounds on each wall of the groove. It seems like teh easiest solution would be to just write SMPTE LTC to one side and something like word clock or black burst on the other. <relurk> -- /+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\-/+\ YankTheChain.com - You can pretend we're not here. That's what I do. http://www.yankthechain.com/ http://www.digitalblack.org/

I read: actually you explain it just great ;) and the rising saw gives me the direction info of course, regards, x -- chris(a)lo-res.org Postmodernism is german romanticism with better http://pilot.fm/ special effects. (Jeff Keuss / via ctheory.com)

On Mon, Oct 07, 2002 at 09:18:38PM +0200, CK wrote: But DJ techniques include manipulating the speed of the record - faster or slower. So if all you do is measure frequency, you won't know whether you've increased the position or the speed. So I think something like the suggestion of stereo-encoding two signals is necessary. That way the speed and direction can always be determinied by looking at the sawtooth wave, e.g. on the left channel, as suggested previously; and the *position* can be determined by comparing the ratio of the sawtooth wave to a time-varying signal on the right channel. Encoding stereo to an LP is no problem - the needle vibrates along two axes. There's a limit to how much stereo separation you can get (I forget, it might be like 40-45 dB) but that shouldn't be too hard to account for. --PW -- Paul Winkler "Welcome to Muppet Labs, where the future is made - today!"

Hi all, it's been some time since my last post but probably you all know the problem(s) with time... Reading the Final Scratch thread, I remembered a similar discussion some months ago. I posted the following scheme ( see below) as a proposal for such a system. The main issues you have here are very similar to the issues present in Telecommunication equipement. The scheme uses some telecom concepts, and probably could be improved even more. Using the right coding techniques, it's possible to retrieve data from a system with SNR even lower than 9dB... Keeping in mind that for example an AM radio broadcast has a SNR of > 60dB, it should be clear that a record provides plenty of data capability. The issue of pitch detection resides, but can be addressed too. The main thing I'm trying to say here is that this problem is very like to the problems in digital telecommunications. And they have solved them. So why not use these techniques? Who's to say that QPSK or so cannot be used on a record? I don't have the time right now, but with a little help of someone with telecom knowledge, it should be possible to create a very good scheme. This thread mentiones the use of a saw waveform, with success... but there are better options, that will result in better performance. I'm aware that all of this is a little vague... use it if you want. or don't use it. Pieter PS: I'm more of an audio guy than a telecom guy, believe me. The only problem is that the people that teach my classes are telecom guys. And telecom is (or was) a big market, so who's to blame them... and now for the original post: (a little telecom knowledge doesn't hurt) (26-jan-2002) ---------------------------------------------------------------------------- ------------ The way Stanton probably syncs (as they support 'needle dropping') is to have some time code on the LP, instead of a sawtooth, which is ok for sync'ing and direction, but doesnt provide 'absolute' time info. It would be better to use a passband digital modulation. That way you can embed some kind of 'timer' in the LP. For example: use a 1000Hz carrier with a AM/FM modulated differential NRZ code. You can then put e.g. every 10ms a number on the disc using the coding. That way, if you decode the modulated signal, you perfectly know where on the disc you are. Let me do the math (so I see if this is possible): Let's say you want a dub-plate of 10min=60000*10ms. So if we use a 16bit number, we have 65536 numbers=+/-11mins. If you use a carrier, you can extract the pitch change from the carrier frequency (you are already doing this, I presume). If you use AM modulation, this is very easy. Assume Amplitude Modulation, On-Off Keying. The bitrate of the signal would then be 16bit/10ms=1600bps, so the bandwidth of the modulated signal is 3200Hz. This means that we would have to shift the carrier to > 4000Hz to keep things easy. Let's say 5000Hz. As the carrier period = 1/5000Hz, the maximal pitch resolution obtainable would be 0.2ms, but that won't happen due to the PC latency. If you would extract pitch from 10 carrier periods, you would have a 2ms minimal delay. As for the binary 'timecode', let's assume we need 5 numbers to make a descision about the correct position (e.g. 5 consecutive numbers needed to make sure the software doesn't get confused when there is a scratch or so) (5nrs*16bit/nr)/1600bps=0.05s=50ms. I would like to meet the DJ that can drop his needle with a resolution of 50ms. To further enhance the system, one could use a more efficient modulation, like using raised cosine pulses instead of the block pulses I made these calculations with. You could also use an error correction code, e.g. Reed-Solomon like used on CD's. etc... This might be a little technical, but I just wanted to explain how I think they did it. And the techniques used are not that new... these are the most simple digital communication techniques. A 2400baud modem uses more sophisticated techniques. The difficulty is applying digital communication theory to a recorded medium... They are actually using the LP as a sort of harddisk, the only difference being that it can't contain a lot of data: 2^16 nrs * 16bit/nr / (8bit per byte) = 131072 bytes (131k) but you can change the plate speed. I see no reason why this system wouldn't work (when enhanced to tolerate dust etc). The detection techniques are well documenten in communications literature (PLL, coherent detection, etc). It's like said before (in the EVO thread): The creativity lies in applying know techniques to a new domain. Anyway, I'd love any feedback on this, I instanly made this up, so I probably missed some major things... cu, Pieter ---------------------------------------------------------------------------- -----------------------

On Mon, Oct 07, 2002 at 12:19:39PM -0700, Lance Blisters wrote: (snip) ... exactly what I just tried to say, but better. -- Paul Winkler "Welcome to Muppet Labs, where the future is made - today!"

On Mon, Oct 07, 2002 at 05:34:59PM +0200, CK wrote: Another interesting tidbit is that, apparantly, Finalscratch is using alsaplayer input plugins for decoding their audio. I do hope they don't violate the GPL in any way. Should call them up sometime... :) Regards, Andy @ alsaplayer.org