rdefabri Posted September 18, 2023 Share Posted September 18, 2023 I'm sure this has been covered ad nauseum, so apologies if it's in another thread. I'm not the most successful at finding stuff, and some of the older threads aren't relevant, particularly in light of the work by folks like @VinsCool and @makary. I am curious about POKEY's high pass (and I think there is some sort of low pass) "filters". IIRC, these are used in sort of an "on/off" fashion, rather than in increments, which leads to my question. Is there a way to create filter sweep type effects, or is that not possible given the on/off nature of the filters? Would make for some cool effects in music if they could be used in a sweeping fashion. Just curious...thx! Quote Link to comment Share on other sites More sharing options...
thorfdbg Posted September 18, 2023 Share Posted September 18, 2023 This is just misinformation - this is not a "high-pass filter" in the sense that it filters in the frequency domain. It is just an AND-gate between two channels, i.e. the output is only high if the output of the original channel and the channel which is included in the high-pass are both 1. There is neither a "low-pass filter". Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 18, 2023 Author Share Posted September 18, 2023 22 minutes ago, thorfdbg said: This is just misinformation - this is not a "high-pass filter" in the sense that it filters in the frequency domain. It is just an AND-gate between two channels, i.e. the output is only high if the output of the original channel and the channel which is included in the high-pass are both 1. There is neither a "low-pass filter". Yes, I am aware, hence "filter" in quotes. I found a document suggesting a "low pass filter", although I question the accuracy since I know there isn't anything like that. I'll try to dig it up. Regardless, my question still stands. Is there some way to make the filter operate in a sweeping fashion? Again, I'm guessing not, but there have been new capabilities uncovered leveraging software, so I'm curious if anything like this has been attempted. Quote Link to comment Share on other sites More sharing options...
Mathy Posted September 18, 2023 Share Posted September 18, 2023 Hello rdefabri Looks like something went wrong when you entered @VinsCool and @makary. Sincerely Mathy Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 18, 2023 Author Share Posted September 18, 2023 24 minutes ago, Mathy said: Hello rdefabri Looks like something went wrong when you entered @VinsCool and @makary. Sincerely Mathy Thanks! Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 18, 2023 Author Share Posted September 18, 2023 Ok this is something like what I am looking for. In the opening of this song, there is kind of a sweeping sound. It’s not quite a filter sweep but sounds similar. @VinsCool - did you help create this? What was done to create that sort of sweep effect? Really cool stuff! Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted September 19, 2023 Share Posted September 19, 2023 what song? you didn't attach, link, or post it. Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 19, 2023 Author Share Posted September 19, 2023 12 hours ago, _The Doctor__ said: what song? you didn't attach, link, or post it. Crud - I was posting that from my phone and must have messed that up...let me find it Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 19, 2023 Author Share Posted September 19, 2023 This isn't the one I tried to post, but this has a similar "sweep". If you listen to the bass line, you can hear the effect: Quote Link to comment Share on other sites More sharing options...
Rybags Posted September 19, 2023 Share Posted September 19, 2023 Timestamp? There seems to be all sorts in that - filters, 1.79 MHz mode on single voice, 15 KHz mode, possibly even 2-tone. Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 19, 2023 Author Share Posted September 19, 2023 2 hours ago, Rybags said: Timestamp? There seems to be all sorts in that - filters, 1.79 MHz mode on single voice, 15 KHz mode, possibly even 2-tone. Right at the beginning you can hear it - from 0:00 - 0:06. The bass line has a sweeping filter sound...there's a full sound that starts to thin out as the filter (seems) to be applied. It sounds like something is happening there incrementally as opposed to on / off. Quote Link to comment Share on other sites More sharing options...
Rybags Posted September 19, 2023 Share Posted September 19, 2023 Not sure that's filter. You can get cancelling of output when channels are in certain states on notes of similar frequency. It looks to be in 15 KHz mode at that point (the video seems to have an overlay of the Altirra audio graphing maybe?) - though you can mix and match master frequencies applied to voices to an extent. Quote Link to comment Share on other sites More sharing options...
Steril707 Posted September 19, 2023 Share Posted September 19, 2023 Yep; i think that's just frequencies cancelling each other out. Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 19, 2023 Author Share Posted September 19, 2023 (edited) 25 minutes ago, Rybags said: Not sure that's filter. You can get cancelling of output when channels are in certain states on notes of similar frequency. It looks to be in 15 KHz mode at that point (the video seems to have an overlay of the Altirra audio graphing maybe?) - though you can mix and match master frequencies applied to voices to an extent. As I suspected, it's NOT filtering, but it sure acts similarly. Perhaps it's accidental, but it is a (somewhat) desirable effect that mimics what a true filter sweep might sound like. So does that answer the question - can you apply the POKEY filter in a dynamic fashion to create sweeping effects? Or is it simply an on / off effect? Edited September 19, 2023 by rdefabri Quote Link to comment Share on other sites More sharing options...
VinsCool Posted September 19, 2023 Share Posted September 19, 2023 The filter was applied at strategic timing, with different frequencies offset to produce that "sweeping effect", which was effectively resetting the channel phases to a known initial position, in order to cancel each others with slight phase offset to allow the filter to create a pulse width modulation effect. Here it was reset with a clock 64khz to improve the pulse width precision, the mode switch was getting masked every beat with the kick drums. Further in the video I was experimenting with various combinations in order to create stable pulse width modulation, which was pretty convincing if you consider that it's difficult to make things sound stable in the first place. 4 1 Quote Link to comment Share on other sites More sharing options...
rdefabri Posted September 19, 2023 Author Share Posted September 19, 2023 5 hours ago, VinsCool said: The filter was applied at strategic timing, with different frequencies offset to produce that "sweeping effect", which was effectively resetting the channel phases to a known initial position, in order to cancel each others with slight phase offset to allow the filter to create a pulse width modulation effect. Here it was reset with a clock 64khz to improve the pulse width precision, the mode switch was getting masked every beat with the kick drums. Further in the video I was experimenting with various combinations in order to create stable pulse width modulation, which was pretty convincing if you consider that it's difficult to make things sound stable in the first place. That is pretty cool and rather effective. Not quite a true filter sweep, but it accomplishes a similar effect IMHO. 1 Quote Link to comment Share on other sites More sharing options...
makary Posted October 1, 2023 Share Posted October 1, 2023 Doing this demo soundtrack years ago I wanted to see to what extend the pulse width / 'filter' / sweeps can be controlled. I got some results but I think @VinsCool has found more interesting ideas and results regarding these 'filter' mysteries. 9 Quote Link to comment Share on other sites More sharing options...
rdefabri Posted October 2, 2023 Author Share Posted October 2, 2023 On 10/1/2023 at 12:15 PM, makary said: Doing this demo soundtrack years ago I wanted to see to what extend the pulse width / 'filter' / sweeps can be controlled. I got some results but I think @VinsCool has found more interesting ideas and results regarding these 'filter' mysteries. What version of RMT are you using? Do you do any post processing or are these played on actual hardware? Great stuff - keep up the good work! Quote Link to comment Share on other sites More sharing options...
+MrFish Posted October 2, 2023 Share Posted October 2, 2023 On 10/1/2023 at 12:15 PM, makary said: Doing this demo soundtrack years ago I wanted to see to what extend the pulse width / 'filter' / sweeps can be controlled. I got some results but I think @VinsCool has found more interesting ideas and results regarding these 'filter' mysteries. I really like all the musical work you've done on the POKEY. Quote Link to comment Share on other sites More sharing options...
makary Posted October 3, 2023 Share Posted October 3, 2023 11 hours ago, rdefabri said: What version of RMT are you using? Do you do any post processing or are these played on actual hardware? Great stuff - keep up the good work! I made a fork of RMT with alternative tuning dedicated to 15kHz. And yes, you can run the tunes on real hardware. No postprocessing. Thanks @MrFish This so-called POKEY 'filter' works like this I believe: Each edge from voice 1 inverts the signal. Each edge from voice 2 sends it low. As you can imagine trying to control this and use musically is pain in the neck 1 Quote Link to comment Share on other sites More sharing options...
VinsCool Posted October 5, 2023 Share Posted October 5, 2023 On 10/1/2023 at 12:15 PM, makary said: Doing this demo soundtrack years ago I wanted to see to what extend the pulse width / 'filter' / sweeps can be controlled. I got some results but I think @VinsCool has found more interesting ideas and results regarding these 'filter' mysteries. This is the song that actually made me understand what was going on with the filter a few years ago, actually! I have been doing now is more or less exactly the same tricks but with additional tweaks learned some time later. This is the very first song I could say for sure used "absolute" control over the pulses, and this is the exact same tricks I have used in the much later Sketch 86 module. On 10/3/2023 at 1:30 AM, makary said: This so-called POKEY 'filter' works like this I believe: Each edge from voice 1 inverts the signal. Each edge from voice 2 sends it low. As you can imagine trying to control this and use musically is pain in the neck This is pretty much the same conclusion I have come to, I still have not fully understood how this stuff works but experimenting with the "Filterchord" sounds really made it even more fun. The generated waveforms are a lot more stable when the intervals are Just right, the more consonant the better. Here's an example of the Filter usage where it produced a "Voice Choir" tone using a Major 10th interval, combined to the regular PWM filter played with the "absolute" manipulations from earlier. I really could go on and on with more examples with the experimentation, but I think we can agree that there is a lot more going on with the filter when you find your ways around using it to produce impossible sounds It's so much fun, but also so much work to get things to sounds good, haha! 1 Quote Link to comment Share on other sites More sharing options...
makary Posted April 28 Share Posted April 28 I think this one shows some interesting usage of 'filters'. The filtered instruments use PWM but mixed with changes in volume envelope. The result is some kind of phaser(?) or flanger(?) effect. BTW: melodic parts are based on 'Moment of Stop' by Dhor. WOBBLE.xex 9 1 Quote Link to comment Share on other sites More sharing options...
olix Posted April 28 Share Posted April 28 ... a really very impressive sound! 1 Quote Link to comment Share on other sites More sharing options...
Rybags Posted April 28 Share Posted April 28 Pretty good. But I do suspect it is a filtered voice pair in conjunction with a low frequency note on the other voice/s. 1 Quote Link to comment Share on other sites More sharing options...
makary Posted April 28 Share Posted April 28 Yes, it is. But there's more to it. The effect becomes present only when specific frequencies and specific loops are set in the filtering channel/instrument. I hope I'll be more precise about it later on. I've just started messing with these settings. So it's more trial and error kind of work at this stage Quote Link to comment Share on other sites More sharing options...
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