4 ms·

My dad bought an Isuzu Impulse in 1985. It had a fancy OEM stereo system with Technics branding, and a button for the driver to toggle the imaging. The button w

My dad bought an Isuzu Impulse in 1985. It had a fancy OEM stereo system with Technics branding, and a button for the driver to toggle the imaging. The button was on the 7-band graphic EQ that game with the car. (I don't think I've ever seen another factory stereo with physical EQ sliders like that.) It was magic, if you were sitting in the driver's seat. Toggling that button made the sound switch from "okay" to "magically spatial." I'm pretty sure that lead to a conversation about how we locate sounds. Also wonder how it was implemented in 1985. I doubt there were DSP chips in there. What's the "simple" way of adding delay to some speakers?

jareklupinski 5y ago
a reaaaaaaaalllllllyyy long wire :P pro audio equipment sometimes used 'bucket brigade' chips to implement a delay line (shame that you can't get them anymore)
- Tempest1981 5y ago
  Also called https://en.wikipedia.org/wiki/Analog_delay_line https://en.wikipedia.org/wiki/Analog_delay_line
  - bellyfullofbac 5y ago
    And they even have this digitally (fiber optic). Relevant Tom Scott: https://www.youtube.com/watch?v=d8BcCLLX4N4 https://www.youtube.com/watch?v=d8BcCLLX4N4
- wgj 5y ago
  Good news. Bucket brigade (BBD) chips are still produced and available from various sources. [0][1] They are used today in a lot of guitar/synth gear. [0] https://www.electrosmash.com/mn3007-bucket-brigade-devices https://www.electrosmash.com/mn3007-bucket-brigade-devices [1] https://www.coolaudio.com/features-page.php?product=V3205SD https://www.coolaudio.com/features-page.php?product=V3205SD They way they work by design, clock noise needs to be filtered out of the final signal, so relatively heavy low pass filtering is standard. The result isn't very hi-fi.
  - jareklupinski 5y ago
    whoa ty! just unblocked a 5-year old project :)
wgj 5y ago
At that time, the most common way to do stereo enhancement was to decrease the L + R component of the stereo signal. [0] L+R/L-R was (and still is) a common way to encode stereo signals, including for FM radio. [1] The impact on the stereo field by just changing the mix of these two components is profound. No signal delay needed. For signals that are simple L and R, sum them to get L+R and difference to get L-R. So you can use this technique on any stereo source. [0] https://www.sweetwater.com/insync/stereo-enhancement-work-more-better/ https://www.sweetwater.com/insync/stereo-enhancement-work-mo... [1] https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM
- function_seven 5y ago
  I may be misremembering—I was a kid at the time—but I distinctly remember the "wow" effect only working if you were sitting in the driver's seat. To me that suggests that the signals were delayed to the nearer speakers to center the sound stage around the driver rather than some arbitrary point above the center console. But looking up photos online, I see the button I was talking about labeled as "Ambience", which kind of suggests the method you're describing. It also turns out that using the Internet to find technical info about a 40-year-old car that was never popular to begin with is very hard!
jasonwatkinspdx 5y ago
> I'm pretty sure that lead to a conversation about how we locate sounds. So, psychoacoustics is incredibly complicated. There's something like 13 different mechanisms that co-operate in sound localization. However, the bulk of it was known quite a bit before 1985, and had nothing to do with the "spatialize me" button on a specific car stereo. There's no simple way to add a delay to some speakers unless you're working in the digital domain. In analog you have two basic choices. With passive components, you build a ladder filter, which is as the name suggests, just a long chain of low pass or all pass filters. Each "rung" only adds group delay on the scale of a couple usec, so these get very big and expensive fast. They also suffer from accumulated imprecision issues. With active components you can create a feedback loop through an op amp. This is how guitar delay pedals work, but the more delay you have the more distortion you introduce. Technically there's a 3rd way: extremely long wires, but that's basically never practical. Thankfully these days everything starts out in the digital domain, so you just need a controllable fifo before the DAC. Entry level home theater receivers have had this since circa 2000.
- noir_lord 5y ago
  > Technically there's a 3rd way: extremely long wires, but that's basically never practical. Did the math, ~170km (assuming 300,000 km/s and speed of light in copper been 90%) - that's a long wire, would also have to be superconducting or very high voltage ;). Whatever room temperature superconductors end up costing Audiophiles will be the early adopters ;).
- function_seven 5y ago
  Hell, even if the premise of the conversation was wrong, I still learned something that day :) DSPs were a thing in the 80s, right? I guess the question is: were they so expensive that it was unlikely to find one in an OEM stereo of a mid-priced car? A sibling comment mentions that this button may have just been a stereo expando kind of thing, rather than localizing the sound stage through signal delays. I'm thinking that may be right, and that I'm misremembering the feature. It would be awesome to find some original owners manuals for the 1985 Impulse that have any mention of this feature. My DDG-fu is failing me right now. Now, which one of those 13 mechanisms is failing on me when the damn cricket keeps "moving" around the room as I try to follow the chirp?
djtriptych 5y ago
My friend had an acura in the 90s with physical EQ sliders. Can't remember if it was OEM or not but my guess is that it was.
TheOtherHobbes 5y ago
The simple way is to add some cross-channel antiphase to both channels. So R = (R - cL), and L = (L - cR) where c << 1. This is very cheap and easy with opamps. It does indeed sound magical, and makes the stereo image expand beyond the speakers. It also does weird things to a mono mixdown and if c is too big you get a hole in the middle. But if you keep c small and use it as the final effect just before the speakers that's not a problem. You could also use BBD[1] chips to add a ms or so of analog delay, but that's less likely because it would have been more complex and expensive. Digital audio delays had appeared in studios by the late 1970s, but they were still more expensive than BBDs in the mid-80s, so unlikely for in-car use. [1] Bucket Brigade Delay

jareklupinski 5y ago

a reaaaaaaaalllllllyyy long wire :P pro audio equipment sometimes used 'bucket brigade' chips to implement a delay line (shame that you can't get them anymore)

Tempest1981 5y ago
Also called https://en.wikipedia.org/wiki/Analog_delay_line https://en.wikipedia.org/wiki/Analog_delay_line
- bellyfullofbac 5y ago
  And they even have this digitally (fiber optic). Relevant Tom Scott: https://www.youtube.com/watch?v=d8BcCLLX4N4 https://www.youtube.com/watch?v=d8BcCLLX4N4
wgj 5y ago
Good news. Bucket brigade (BBD) chips are still produced and available from various sources. [0][1] They are used today in a lot of guitar/synth gear. [0] https://www.electrosmash.com/mn3007-bucket-brigade-devices https://www.electrosmash.com/mn3007-bucket-brigade-devices [1] https://www.coolaudio.com/features-page.php?product=V3205SD https://www.coolaudio.com/features-page.php?product=V3205SD They way they work by design, clock noise needs to be filtered out of the final signal, so relatively heavy low pass filtering is standard. The result isn't very hi-fi.
- jareklupinski 5y ago
  whoa ty! just unblocked a 5-year old project :)

wgj 5y ago

At that time, the most common way to do stereo enhancement was to decrease the L + R component of the stereo signal. [0] L+R/L-R was (and still is) a common way to encode stereo signals, including for FM radio. [1] The impact on the stereo field by just changing the mix of these two components is profound. No signal delay needed. For signals that are simple L and R, sum them to get L+R and difference to get L-R. So you can use this technique on any stereo source. [0] https://www.sweetwater.com/insync/stereo-enhancement-work-more-better/ https://www.sweetwater.com/insync/stereo-enhancement-work-mo... [1] https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM

function_seven 5y ago
I may be misremembering—I was a kid at the time—but I distinctly remember the "wow" effect only working if you were sitting in the driver's seat. To me that suggests that the signals were delayed to the nearer speakers to center the sound stage around the driver rather than some arbitrary point above the center console. But looking up photos online, I see the button I was talking about labeled as "Ambience", which kind of suggests the method you're describing. It also turns out that using the Internet to find technical info about a 40-year-old car that was never popular to begin with is very hard!

jasonwatkinspdx 5y ago

> I'm pretty sure that lead to a conversation about how we locate sounds. So, psychoacoustics is incredibly complicated. There's something like 13 different mechanisms that co-operate in sound localization. However, the bulk of it was known quite a bit before 1985, and had nothing to do with the "spatialize me" button on a specific car stereo. There's no simple way to add a delay to some speakers unless you're working in the digital domain. In analog you have two basic choices. With passive components, you build a ladder filter, which is as the name suggests, just a long chain of low pass or all pass filters. Each "rung" only adds group delay on the scale of a couple usec, so these get very big and expensive fast. They also suffer from accumulated imprecision issues. With active components you can create a feedback loop through an op amp. This is how guitar delay pedals work, but the more delay you have the more distortion you introduce. Technically there's a 3rd way: extremely long wires, but that's basically never practical. Thankfully these days everything starts out in the digital domain, so you just need a controllable fifo before the DAC. Entry level home theater receivers have had this since circa 2000.

noir_lord 5y ago
> Technically there's a 3rd way: extremely long wires, but that's basically never practical. Did the math, ~170km (assuming 300,000 km/s and speed of light in copper been 90%) - that's a long wire, would also have to be superconducting or very high voltage ;). Whatever room temperature superconductors end up costing Audiophiles will be the early adopters ;).
function_seven 5y ago
Hell, even if the premise of the conversation was wrong, I still learned something that day :) DSPs were a thing in the 80s, right? I guess the question is: were they so expensive that it was unlikely to find one in an OEM stereo of a mid-priced car? A sibling comment mentions that this button may have just been a stereo expando kind of thing, rather than localizing the sound stage through signal delays. I'm thinking that may be right, and that I'm misremembering the feature. It would be awesome to find some original owners manuals for the 1985 Impulse that have any mention of this feature. My DDG-fu is failing me right now. Now, which one of those 13 mechanisms is failing on me when the damn cricket keeps "moving" around the room as I try to follow the chirp?

djtriptych 5y ago

My friend had an acura in the 90s with physical EQ sliders. Can't remember if it was OEM or not but my guess is that it was.

TheOtherHobbes 5y ago

The simple way is to add some cross-channel antiphase to both channels. So R = (R - cL), and L = (L - cR) where c << 1. This is very cheap and easy with opamps. It does indeed sound magical, and makes the stereo image expand beyond the speakers. It also does weird things to a mono mixdown and if c is too big you get a hole in the middle. But if you keep c small and use it as the final effect just before the speakers that's not a problem. You could also use BBD[1] chips to add a ms or so of analog delay, but that's less likely because it would have been more complex and expensive. Digital audio delays had appeared in studios by the late 1970s, but they were still more expensive than BBDs in the mid-80s, so unlikely for in-car use. [1] Bucket Brigade Delay