Re: [PD] change samplerate locally
On Sun, Mar 15, 2009 at 2:44 AM, hard off hard@gmail.com wrote: to re-create the sound of a dx7 i need to change samplerate from my default (44.1khz) to 28khz. globally changing pd's samplerate to 28khz has the intended effect, but i want to be able to run other patches at 44.1khz while running my dx7 at 28khz. One thing that occurs to me is that the quality of the reconstructed sound has more to do with the interpolator rather than the sample rate. The actual output is an analog signal which is obtained by interpolating samples. Most audio systems use linear interpolation, which has characteristic spectral characteristics. A low-end or possibly obsolete system may use sample-and-hold rather than interpolation. Probably, there's a high-frequency sizzle that you want to emulate here. To get that full sound (an analog signal), there's a freq domain transformation that should work. It comes from the linear interpolator. It actually leaves some sound in the range from 14kHz to 22.05kHz. To reproduce the effect, you would fold over frequencies from 5.95kHz to 14 kHz into 14kHz to 22.05kHz. Then you would apply the spectrum of the interpolator, which will reduce but not eliminate the high frequencies. I haven't worked it all out. That's as far as I got this weekend. Chuck i naively tried adding this construct to the output, but the sound is completely wrong: (if it doesn't show, the phasor~ is connected to the right inlet of the [samplehold~]) [inlet~] [phasor~ 28000] | | [samplehold~] | [outlet~] i thought about it for a bit, and i understand why that doesn't work, but i can't think of another solution. is there some way i can 'mimic' 28khz samplerate while running pd at 44.1? or even better, is there some way to locally set the samplerate for a patch? i tried messing round with [block~] but i can't make it do what i need. also, i need to mimic a 12bit DAC~ too. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
One thing that occurs to me is that the quality of the reconstructed sound has more to do with the interpolator rather than the sample rate. i have a feeling that because the synth has non-bandlimited oscillators, that the sample rate itself is pretty important, or more importantly, the aliasing effect it has is very important. i think that that reason why 28khz is sounding 'better' than 44.1 is because of more high frequencies folding back over and thickening the sound up in the low end. i could be totally wrong, but that's what it sounds like. 44.1khz is 'thin and wimpy', but at 28khz it's a thicker, fuller sound. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
so if those aliasing effects are going to help, then maybe a big step will be to ADD aliasing. there are a couple of suggestions here: http://www.music.columbia.edu/pipermail/music-dsp/2002-March/047953.html and here: http://www.music.columbia.edu/pipermail/music-dsp/2002-March/047966.html i'll give them a go tomorrow. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
i had a minor breakthrough. upsampling my signal path, by using [block~ 64 1 2] has the same effect on the sound as lowering pd's global sample rate to 22050. not perfect, and to me it defies logic, but certainly a lot closer to the 28khz sound than the 44.1khz sound was getting. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
Hmm. I thought the DX7 was ~57khz, anyway: http://www.maths.abdn.ac.uk/~bensondj/html/Chowning.html On Tue, Mar 17, 2009 at 2:35 AM, hard off hard@gmail.com wrote: i had a minor breakthrough. upsampling my signal path, by using [block~ 64 1 2] has the same effect on the sound as lowering pd's global sample rate to 22050. not perfect, and to me it defies logic, but certainly a lot closer to the 28khz sound than the 44.1khz sound was getting. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
so, i thought about this more, and realized that 28hz is quite close to being 2/3 of 44.1 so, it MIGHT be enough to do the following: for every 3 samples, output the first sample, the second sample, and then instead of playing the 3rd sample, repeat the second sample. so, if my block looks like: 0.597, 0.604, 0.628, 0.651.. then the output block would be 0.597, 0.604, 0.604, 0.651 ... i still have no idea how i would do that. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
hard off wrote: to re-create the sound of a dx7 i need to change samplerate from my default (44.1khz) to 28khz. globally changing pd's samplerate to 28khz has the intended effect, but i want to be able to run other patches at 44.1khz while running my dx7 at 28khz. I think that the sound card decides what sample rates you can use, you probably can get 22.5 and 11.25 but not 28. A clean resampling usually would mean sampling at a common multiple of 28kHz and 44.1kHz and then downsampling again, not really feasible with Pd. i naively tried adding this construct to the output, but the sound is completely wrong: (if it doesn't show, the phasor~ is connected to the right inlet of the [samplehold~]) [inlet~] [phasor~ 28000] | | [samplehold~] | [outlet~] i thought about it for a bit, and i understand why that doesn't work, but i can't think of another solution. is there some way i can 'mimic' 28khz samplerate while running pd at 44.1? or even better, is there some way to locally set the samplerate for a patch? i tried messing round with [block~] but i can't make it do what i need. Unless you're looking for aliasing artifacts, wouldn't it be easier to use a multi-pole low-pass filter at around 14kHz? also, i need to mimic a 12bit DAC~ too. For that you could multiply the samples by 2048 (for bipolar signal) and then divide them modulo 2048, like this: [*~ 2048] | [expr~ $v1%2048] | [/~ 2048] | [dac~] Martin ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
hi martin, thanks for taking the time to reply. i can set pd to whatever samplerate i want in media-audio settings. i just checked again going through a whole bunch of values between 22050 and 44100 and they all work. my problem is that the samplerate is global, and i need it only to be local. i think the 'solution' i suggested in my 2nd post is going to be the way to do it, but i just don't know how to do that. [*~ 2048] | [expr~ $v1%2048] | [/~ 2048] thanks. that's what i had done originally, but i couldn't hear any effect. i guess if i really want 12-bit sound in pd, i'd have to use that construct after each and every calculation in the signal chain. seems a fair bit of overkill just to make the sound WORSE though! ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
actually, i just checked and that method i suggested before doesn't work at all. it's the same as the [phasor~ 28000] - [samphold~] effect. martin, i missed this part of your mail before: Unless you're looking for aliasing artifacts, wouldn't it be easier to use a multi-pole low-pass filter at around 14kHz? i just tried that, and i guess what i need must be the aliasing artifacts. ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
Re: [PD] change samplerate locally
hard off wrote: hi martin, thanks for taking the time to reply. i can set pd to whatever samplerate i want in media-audio settings. i just checked again going through a whole bunch of values between 22050 and 44100 and they all work. Yes you're right. I should have checked first ;) Maybe writing into a table at 44100 and using [tabread4~] with a signal that is quantized to the ratio of sample rates would work? my problem is that the samplerate is global, and i need it only to be local. i think the 'solution' i suggested in my 2nd post is going to be the way to do it, but i just don't know how to do that. [*~ 2048] | [expr~ $v1%2048] | [/~ 2048] thanks. that's what i had done originally, but i couldn't hear any effect. i guess if i really want 12-bit sound in pd, i'd have to use that construct after each and every calculation in the signal chain. seems a fair bit of overkill just to make the sound WORSE though! Well 12-bit sound is pretty good, as good as audio cassette with no dolby. You should try replacing 2048 with 128 or less to hear true lo-fi. Martin ___ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management - http://lists.puredata.info/listinfo/pd-list
