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Post by svart on May 11, 2021 8:59:27 GMT -6
I suppose if there is a fundamental below the filter with harmonic content above the filter you could end up with out-of-phase higher order products. Practically speaking I don't know what you do with that information or how you use it though - haha. You do! I deal with it occasionally. Sometimes you have a harmonic that seems to either be lower or higher than it should be despite it being well inside the cut band of a filter. I usually find that sweeping the incident signal will produce a "lumpy" (for lack of a better term) harmonic profile that follows the filter pole overlaps. This is caused by the physical limitations of the components not being ideal. Sometimes you just have a single spot where a harmonic will jump out. Sometimes adjusting the values of the filter poles fixes it, sometimes adding a specific zero to the filter for that one region is the fix. Sometimes I lobby the marketing guys to change the specs instead, lol.
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Post by ragan on May 11, 2021 9:01:54 GMT -6
To svart’s comment about algebra vs calculus, one of the most amazing things (to me) in the math of electricity is that you can use transforms to tailor how you analyze something. In the time domain, even a relatively simple RLC circuit will generate/necessitate a pretty gnarly differential equation which is a pain in the ass to solve. You can use a Laplace transform to translate it all to the frequency domain and solve it purely by algebra, and then transform your solution back to the time domain. It’s amazing.
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Post by ragan on May 11, 2021 9:05:44 GMT -6
Take this guy for instance. It's a 1.8G LPF made from a cascading multiple poles of LC, perhaps on the order of 15-20 poles. View AttachmentYou'll notice that the rolloff at 1.8GHz is high, but then it meanders back up around 6-7GHz. This can be modeled as the phase of each LP pole finally returning to a value that does not nullify. Could you elaborate on how this is a LPF? The insertion loss in dB looks kind of band-pass-y and the standing wave ratio as a function of frequency looks like a high pass. But I’m a newb so... And does that response mean that in the transfer function, you’d find a zero up around 7.5GHz?
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Post by gravesnumber9 on May 11, 2021 9:10:36 GMT -6
Maybe I got it backwards. Or maybe I didn't say it right. What I'm saying is that if my EQ is applied at, say, 10khz, that would be less impactful in terms of phase shift because it's only the frequencies above that that get impacted, correct? Or is it still worse because of the shorter wavelength. Just kind of wondering if there's a "safer" EQ range in terms of drastic boosts/cuts. And yes, I get that it's really all just what sounds good is good and that some phase shifts might sound good... still wondering though. There's even ways to figure this stuff out using different types of math such as calculus and algebra and you'll find folks that prefer doing things in different ways too. Personally I excelled at algebra so just about everything I do comes from algebraic equations and I avoid calculus whenever possible, lol. This describes my experience with higher math nicely. My pursuit of the hard sciences ended when I realized that, while calculus and even higher math is fascinating in the abstract, it doesn't personally engage me. Now... if someone had told me when I was 14 "Hey, you see that Portastudio you love so much? You know that you could be the person who makes stuff like that?" my life could have taken a much different path. It somehow never occurred to me that human beings actually figure this stuff out and build it. I thought it just showed up under a Christmas tree.
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Post by svart on May 11, 2021 9:54:42 GMT -6
Take this guy for instance. It's a 1.8G LPF made from a cascading multiple poles of LC, perhaps on the order of 15-20 poles. View AttachmentYou'll notice that the rolloff at 1.8GHz is high, but then it meanders back up around 6-7GHz. This can be modeled as the phase of each LP pole finally returning to a value that does not nullify. Could you elaborate on how this is a LPF? The insertion loss in dB looks kind of band-pass-y and the standing wave ratio as a function of frequency looks like a high pass. But I’m a newb so... And does that response mean that in the transfer function, you’d find a zero up around 7.5GHz? Look at the Y scale of the graph.. the graph is shown in dB loss increasing upwards.
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Post by ragan on May 11, 2021 10:02:29 GMT -6
Could you elaborate on how this is a LPF? The insertion loss in dB looks kind of band-pass-y and the standing wave ratio as a function of frequency looks like a high pass. But I’m a newb so... And does that response mean that in the transfer function, you’d find a zero up around 7.5GHz? Look at the Y scale of the graph.. the graph is shown in dB loss increasing upwards. Right, ok. Thanks. I guess I should have said bandstop, since it’s loss on the Y axis. But it never quite settles back down to where it is at the lower frequencies so I guess that’s still low pass behavior.
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Post by ragan on May 11, 2021 10:25:17 GMT -6
svart so does the VSWR response in that graph mean that, as you go up in frequency (especially from ~2-3.5GHz), there is a larger mismatch between the load and the transmission line? Because (I think?) for a given voltage reflection coefficient, SWR is just a ratio of the max to the min?
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Post by stormymondays on May 11, 2021 10:31:41 GMT -6
Today I had the rare occasion to remix a track that I had mixed for a time sensitive project that didn’t come to be. So, instead of recalling all the hardware, I took the chance of taking off all the HPF and redo the mix from almost scratch. I’m liking it!!! I’ll let you know if it turns into a muddy mess or if it gets that huge deep sound I’m chasing after... Quoting myself!!! 😂 By the way, fascinating discussion even though hard maths are above my pay grade. This turned out to be a fantastic mix. It beats the original by a mile. It’s not just the lack of HPF but I’ve totally changed my attitude towards the low frequencies. It also translates beautifully from the studio to the car to the diminutive mini Bluetooth speaker! I think I can share both mixes in a couple weeks maybe and we can have a laugh at my initial mix.
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Post by svart on May 11, 2021 11:23:42 GMT -6
svart so does the VSWR response in that graph mean that, as you go up in frequency (especially from ~2-3.5GHz), there is a larger mismatch between the load and the transmission line? Because (I think?) for a given voltage reflection coefficient, SWR is just a ratio of the max to the min? Yep, that's pretty much it. It's important to further detail that the max/min ratio is the difference of the incident signal and the standing wave that's developed. However, Return Loss (S11 for forward RL, S22 for reverse RL) is the direct measurement of the reflection in that it reports the delta dB from the incident signal to the reflected signal. They both measure the same thing, the discontinuities between the source and the load, but do so in different ways. As for the graph, it's telling you that the filter becomes more reflective at frequencies that it's rejecting.
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Post by svart on May 11, 2021 11:30:22 GMT -6
Look at the Y scale of the graph.. the graph is shown in dB loss increasing upwards. Right, ok. Thanks. I guess I should have said bandstop, since it’s loss on the Y axis. But it never quite settles back down to where it is at the lower frequencies so I guess that’s still low pass behavior. It would be band-stop in the broadest sense. The graph is likely de-embedded from a calibrated test jig. in reality the physical parasitics of the interconnects, the PCB materials and the cable will all conspire to roll off the top end. But as a point of interest, to see 10GHz you really need 20GHz bandwidth and if you're spending the thousands of dollars it would take to get 20GHz rated PCB materials (ceramic most likely), then you aren't concerned with this LPF and you're absolutely using distributed element filters instead. At 20GHz the end-cap impedance and the solder pad capacitance would be murdering your high frequencies anyway!
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Post by jmoose on May 11, 2021 13:45:22 GMT -6
Right, ok. Thanks. I guess I should have said bandstop, since it’s loss on the Y axis. But it never quite settles back down to where it is at the lower frequencies so I guess that’s still low pass behavior. It would be band-stop in the broadest sense. The graph is likely de-embedded from a calibrated test jig. in reality the physical parasitics of the interconnects, the PCB materials and the cable will all conspire to roll off the top end. But as a point of interest, to see 10GHz you really need 20GHz bandwidth and if you're spending the thousands of dollars it would take to get 20GHz rated PCB materials (ceramic most likely), then you aren't concerned with this LPF and you're absolutely using distributed element filters instead. At 20GHz the end-cap impedance and the solder pad capacitance would be murdering your high frequencies anyway! Ok. Lets pretend your Rick and I'm Morty... and that what you said there is absolutely true and makes perfect sense. Wrapping things back around to a practical level, how does any of it translate to getting a great kick drum sound? Something which I'll admit is highly debatable and nobody has been able to agree upon since the dawn of time. Its all well & good to talk about the response time of electrolytic vs ceramic capacitors, solder capacitance and all that... but what does any of it have to do with making a better sounding record? Somehow we got lost in the weeds. Or at least I did.
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Post by notneeson on May 11, 2021 15:15:43 GMT -6
It would be band-stop in the broadest sense. The graph is likely de-embedded from a calibrated test jig. in reality the physical parasitics of the interconnects, the PCB materials and the cable will all conspire to roll off the top end. But as a point of interest, to see 10GHz you really need 20GHz bandwidth and if you're spending the thousands of dollars it would take to get 20GHz rated PCB materials (ceramic most likely), then you aren't concerned with this LPF and you're absolutely using distributed element filters instead. At 20GHz the end-cap impedance and the solder pad capacitance would be murdering your high frequencies anyway! Ok. Lets pretend your Rick and I'm Morty... and that what you said there is absolutely true and makes perfect sense. Wrapping things back around to a practical level, how does any of it translate to getting a great kick drum sound? Something which I'll admit is highly debatable and nobody has been able to agree upon since the dawn of time. Its all well & good to talk about the response time of electrolytic vs ceramic capacitors, solder capacitance and all that... but what does any of it have to do with making a better sounding record? Somehow we got lost in the weeds. Or at least I did. Those guys are a working EE and an EE student, thus the math. I bet both of them use filters and trust their ears. I’ll just add, I like some sub in my kick. Royer 121 out front or a few dB on the low band of a 550a or SSL make me smile.
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Post by Guitar on May 11, 2021 15:25:16 GMT -6
Time for a skins and shirts game, haha! Great thread.
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Post by svart on May 11, 2021 15:47:20 GMT -6
It would be band-stop in the broadest sense. The graph is likely de-embedded from a calibrated test jig. in reality the physical parasitics of the interconnects, the PCB materials and the cable will all conspire to roll off the top end. But as a point of interest, to see 10GHz you really need 20GHz bandwidth and if you're spending the thousands of dollars it would take to get 20GHz rated PCB materials (ceramic most likely), then you aren't concerned with this LPF and you're absolutely using distributed element filters instead. At 20GHz the end-cap impedance and the solder pad capacitance would be murdering your high frequencies anyway! Ok. Lets pretend your Rick and I'm Morty... and that what you said there is absolutely true and makes perfect sense. Wrapping things back around to a practical level, how does any of it translate to getting a great kick drum sound? Something which I'll admit is highly debatable and nobody has been able to agree upon since the dawn of time. Its all well & good to talk about the response time of electrolytic vs ceramic capacitors, solder capacitance and all that... but what does any of it have to do with making a better sounding record? Somehow we got lost in the weeds. Or at least I did. Absolutely nothing! Dudes and dudettes have been making hits by twisting knobs and moving on and don't give any thought about how the sausage is made..
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Post by sagefields on May 11, 2021 16:34:21 GMT -6
Today I had the rare occasion to remix a track that I had mixed for a time sensitive project that didn’t come to be. So, instead of recalling all the hardware, I took the chance of taking off all the HPF and redo the mix from almost scratch. I’m liking it!!! I’ll let you know if it turns into a muddy mess or if it gets that huge deep sound I’m chasing after... Quoting myself!!! 😂 By the way, fascinating discussion even though hard maths are above my pay grade. This turned out to be a fantastic mix. It beats the original by a mile. It’s not just the lack of HPF but I’ve totally changed my attitude towards the low frequencies. It also translates beautifully from the studio to the car to the diminutive monk Bluetooth speaker! I think I can share both mixes in a couple weeks maybe and we can have a laugh at my initial mix.
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Post by jmoose on May 11, 2021 16:54:43 GMT -6
Absolutely nothing! Dudes and dudettes have been making hits by twisting knobs and moving on and don't give any thought about how the sausage is made.. I certainly don't think about it too much unless the sausage lets out the magic smoke... Then sometimes I can fix it with the magic BBQ wand and sometimes its gotta go back to the pork store for a professional re-stuffing.
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Post by ragan on May 11, 2021 17:32:15 GMT -6
Ok. Lets pretend your Rick and I'm Morty... and that what you said there is absolutely true and makes perfect sense. Wrapping things back around to a practical level, how does any of it translate to getting a great kick drum sound? Something which I'll admit is highly debatable and nobody has been able to agree upon since the dawn of time. Its all well & good to talk about the response time of electrolytic vs ceramic capacitors, solder capacitance and all that... but what does any of it have to do with making a better sounding record? Somehow we got lost in the weeds. Or at least I did. Absolutely nothing! Dudes and dudettes have been making hits by twisting knobs and moving on and don't give any thought about how the sausage is made.. What, you don't use 30km mic cables to record bands whose songs are exclusively HF square wave pulses??? Cause I can hardly get anything tracked without getting into transmission line theory. I keep a copy of the telegrapher's equations taped to my kick drum, I dunno how I'd get any work done otherwise.
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Post by jampa on May 11, 2021 21:10:25 GMT -6
0Hz, but I try to avoid it Cheers
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Post by Quint on May 13, 2021 22:09:39 GMT -6
Well this has certainly taken a turn into some deep technical stuff that makes my eyes glaze over like I'm sitting in calculus class again. I don't have any reference on designing circuits or programming plugins... I'm just a simple caveman who's been living in studios & making records for 20 years. From a practical perspective, when recording guitars I can easily say my favorite EQ in the room... the best, meaning the least offensive and most effective available for that situation is the EQ on the amp head. The second best EQ is moving the microphone. Seems that for whatever reasons when I need to turn to outboard EQ, the usual suspects to make a sound at a certain point things get weird. And sometimes offensive, like sand on my ears. Don't get me wrong sometimes I use the whole range and go +15... it's available for a reason but not everything sounds good there and I'm just as happy to not need it. +1 on the best guitar eq being the eq on the amp, followed by mic choice.
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Post by askomiko on May 14, 2021 2:00:25 GMT -6
There's even ways to figure this stuff out using different types of math such as calculus and algebra and you'll find folks that prefer doing things in different ways too. Personally I excelled at algebra so just about everything I do comes from algebraic equations and I avoid calculus whenever possible, lol. This describes my experience with higher math nicely. My pursuit of the hard sciences ended when I realized that, while calculus and even higher math is fascinating in the abstract, it doesn't personally engage me. Now... if someone had told me when I was 14 "Hey, you see that Portastudio you love so much? You know that you could be the person who makes stuff like that?" my life could have taken a much different path. It somehow never occurred to me that human beings actually figure this stuff out and build it. I thought it just showed up under a Christmas tree. I was on my way to become a physics teacher, right until the heavy hitter maths started appearing everywhere... "Screw that, I just wanted to blow stuff up!"
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Post by EmRR on May 15, 2021 16:10:02 GMT -6
This may elucidate or confuse. Frequency response changes on top, phase response on bottom.
Better watched on Youtube for size.
A mix of new transformerless 'C' based and old transformer coupled types, some using 'LC' methods. Phase does what phase does, with respect to frequency, regardless of type.
0:00 Bereich03 HC-LC 12dB/oct HPF, 6 and 12dB/oct LPF
1:05 Analog Allstars Pultec various shapes, low to high, including the 'famous' boost/cut on the lows. You can see the phase impact of the transformers at the top and bottom of the range when it's flat.
3:09 API 550A various shapes, including the hpf (I disabled the LPF portion). Ditto on the transformer
5:09 Langevin 251A the couple things they do
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Post by Pueblo Audio on May 17, 2021 14:01:17 GMT -6
When we watch football, we measure the balls movements in yards. When we measure the diameters of vinyls discs we measure in inches. We use the most fitting unit of measure most appropriate to the scale of the situation. When talking about FX delays in music (echos, guitar pedals) the scale lends to be expressed in seconds or milliseconds. When we talk about DSP latency the scale is in samples. When we talk about signal delays who’s durations are comparable to the wavelength of a signal, the scale is in degrees of phase. It takes 360 degrees to complete one cycle, or phase, of a periodic waveform (like a sine wave). For example, take ‘A’ 440Hz which is 440 cycles per second. One complete cycle has a wavelength of 2.27ms. If we divide one cycle by 360 degrees then one degree = .0063ms. (Your not gonna hear kind of delay in a balloon pop video so forget that red herring). Because of the scale, it can be easier here to express in degrees and avoid the decimal places. Now back to phase SHIFT. This is always a relative term. For HPF we are interested in the phase shift (small time delay) of the overtones *RELATIVE* to their fundamental. We are interested because this is a real and audible form of distortion called Deviation from Linear Phase. Without the HPF the overtones are time aligned to their fundamental (Linear Phase). But with a HPF the overtones get shifted in time (measured in degrees). Each overtone will become misaligned , more and more, depending on their frequency. 2nd partial more than the first, 3rd more than the 2nd, and so on. Take note that these hollowed, smeared tonalities will be heard ABOVE the cut off frequency! I hope that helps So this sounds like the issue is worse the lower the frequency, right? If it's a cascading effect with each overtone. So, for example, an aggressive LPF might be less likely to cause such issues. Not exactly. The phase shifts which occur above the cut-off frequency have a limited range. Depending on the design, that range may be as high as 10x the cut-off freq. for example, a 45Hz HPF might shift phase as high as 450Hz. Above 450Hz the phase response will return to linear. So if you slap that 45Hz HPF on, say, a piccolo then we would not expect to hear any phase distortion. But a 45Hz filter on a Bass will skew almost every note the bassist will likely play during a typical song. A good part of the vocal range would also be effected. Etc..
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Post by gravesnumber9 on May 17, 2021 15:09:07 GMT -6
So this sounds like the issue is worse the lower the frequency, right? If it's a cascading effect with each overtone. So, for example, an aggressive LPF might be less likely to cause such issues. Not exactly. The phase shifts which occur above the cut-off frequency have a limited range. Depending on the design, that range may be as high as 10x the cut-off freq. for example, a 45Hz HPF might shift phase as high as 450Hz. Above 450Hz the phase response will return to linear. So if you slap that 45Hz HPF on, say, a piccolo then we would not expect to hear any phase distortion. But a 45Hz filter on a Bass will skew almost every note the bassist will likely play during a typical song. A good part of the vocal range would also be effected. Etc.. Ahhh... that's very helpful. So throwing a HPF to just take care of rumble/noise/etc on an instrument with a higher frequency fundamental seems fairly low risk in terms of unwanted phase issues up the spectrum. Is that correct?
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Post by Guitar on May 18, 2021 9:56:37 GMT -6
Makes me think of a hi hat, which is basically white noise anyway. Don't think it would be a big deal to use a strong high pass there.
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Post by stormymondays on May 24, 2021 11:07:50 GMT -6
I feel a bit self-conscious posting this but here's the mix I did with no HPF: distrokid.com/hyperfollow/stormymondays/forever-youngI love how it turned out. Sometime this week I'll get from the studio the old mix (made two years ago) and the current one and post them on a Dropbox folder. Of course I'm a better mixer now, and I have some extra hardware I didn't have then, but it's still an interesting comparison. I'm also the producer, singer and guitarist, so please be gentle with any criticism...
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