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Comment by scrumper | Hacker News Reader

Article doesn't mention one of the more interesting (to me) aspects which was how feedback was avoided. The solution is elegant: each vocal microphone is doubled, meaning there are two at each position. The phase is inverted on one of them, the singer sings into only one, and both are sent to the speakers via their channel's amp.

The effect of that setup is that only the difference between the two microphones is amplified; common signal in both (i.e. the sound coming out of the speakers) is nulled out, but the difference signal (the voice) makes it through. It apparently wasn't quite perfect but was absolutely a lot better than wailing feedback.

The thing that made it sound so good was that any given speaker only reproduces a single source, but the article touches on that. The mic arrangement I described is simply what makes it possible.

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While it's true that they did that and why, I'd ultimately chalk it up as more of a flaw than a feature. Vocals never sounded great on wall of sound shows because they could never sing perfectly into one mic. This can be confirmed by listentng to soundboard tapes of the shows, and comparing them with ones a year or two either side - the full on Wall was only used for about a year.

While the WoS laid much of the groundwork for how modern PAs are designed and operated, it was more of a white elephant than anything, and many of it's actual ideas were discarded. It was totally impractical to tour with and they lost money doing so. The only real technical legacy it has is of using coherent phased line arrays.

Really it's whole reason for existence (getting a coherent, in phase, non-canceled signal at an extended distance from the stage) isn't even relevant, as these days secondary speaker arrays with delay lines (to sync them perfectly with the mains) is almost childs play. Literally plug and play. Modern PAs can self-tune the whole system just from playing a short burst of white noise through the system, and listening for the response.

Well, yeah, compared to today it's not great but no one had tried anything like that before. They delayed the sound to distant speakers with tape delay. It's cool as shit and was the groundwork for how we do things today.

It's like saying relay computers were dumb... Boolean logic was new and no one had ever attempted stuff like that before.

No, the whole point of the WoS was that there were no distant speakers. Everything was single sourced, to the point where each speaker only carried a single instrument.

I know you probably know, but:

    each speaker only carried a single instrument.

Each vertical stack of speakers only carried a single instrument; not each individual speaker.

The routing wasn't nessisarily full spectrum though. There were a lot of crossovers in use.

I also believe I heard some of the precussion mics were targetting only one or two speakers.

At least in the case of the speakers for Jerry, they had a a seperate McIntosh hi-fi amp for each speaker, being fed out of a Fender-derived preamp and a many-way splitter. Owsley basically bought the every one that model amp that was in stock at dealers on the west coast. Hundreds of thousands of dollars just on those amps - they were something like 2 or 3k a pop even then.

The only reason they were even able to afford in the first place was that Owsley (Yeah that Owsley, who was also their primary sound engineer) had so much illegal cash from a decade of making most of the LSD consumed in the United States. Band never even paid for most it. It was more this crazy idea Owsley had and mostly paid for that they kind of rolled with.

That sort of thing was more than a bit of a pattern in that camp, and was a large part of the band's downfall. It got to a point where it seemed like half of Marin county was on the payroll, and there was so much money going out that they had to tour constantly, wether they wanted to or not. The heavy touring clearly had a major toll on Jerry both physically and mentally. A two or three year hiatus around '91 or '92 would have done him (and probably some of the other guys) a world of good.

They definitely used distant speakers, but yeah, not part of the WoS. I'm just saying that was cutting edge at the time.

Not exactly: the wall of sound was only set up on stage. However, you could hear the music extremely clearly 1/4 mile away, due to the coherence. The delay towers were used before the WoS.

(I assume you're aware, but for the larger audience)... the grateful released an album "Two From the Vault" which was a soundboard recording... but the original soundboard had huge phase cancellation errors due to microphone placement. To recover it, some 20+ years later, with digital tech, the sound engineers could recover the original signal using some clever FFT and phasing very similar to what you describe modern secondary arrays use to self-tune.

Ironically i haven't really listened to most of the official live albums much. I tend to just go straight to the board tapes, which often sound better due to having a few decades of technological advancement - many were transferred in the 90s or 2000s. Of course they didn't have then what we have now, but even consumers by then had access to software for things like mastering that would have made any 70's engineer drool - certain kinds of repairs are much more easily done digitally - back in the day cutting out a spot of stactic or a mic pop involved literal tape and razor blades.

Two From The Vault isn't a "official live album", it's a soundboard that was shelved for decades due to the quality of the recording. I got this album on CD when I was in college (early 90s) and didn't have access to high quality taping equipment, and soundboards from the late 60s were very rare. The audio quality is absolutely excellent (I am just relistening to it now, there's only tiny background hiss, excellent clarity on all the instruments, decent vocals, and only a bit of high-volume distortion on the guitar and bass). It's also a nice counterpoint to the original of the "From The Vault" series, One From The Vault, which was recorded years later under ideal conditions and the band had been practicing extensively.

Much has changed from the days when we had to implement balanced binary trees of tapes (analog tape copies were lossy, so you wanted to minimize the total depth of copies).

Oooh, thank you for sending me down memory lane.

(I took part in lots of tape trees back in the nineties -mostly Neil Young, with a good helping of Grateful Dead and occasionally some Phish thrown in for good measure. Then CD-R became a thing and we did lots of those for blanks+postage. Good times! (I even did DAT trees, as I had three (!) DA-P1s gifted from a local radio station going out of business)

I once got called down to the customs authority to explain what I was up to - they noted I got loads and loads and LOADS of seemingly innocent recording media in the mail, only to ship them out again at a later date.

Nothing showed up when they inspected the packages for drugs, so if I didn't mind - would I PLEASE explain what was going on?

> Vocals never sounded great at wall of sound shows

It was Donna.

Harsh

Accurate

hahaha, no better way to be snapped back into reality than hearing the wild calls of a screeching possum

I cannot read this comment without hearing "Playing in the Band". Now that part is stuck in my head all day, thanks.

apologies for the lack of whoaaa yaaa yay ya a trigger warning

lol! This made my day. To be fair, I love a good Donna tune when she sings actual lyrics. Playin' was always an excuse to just be... a screeching possum is the best I've ever heard it. Whatever, it's rock and roll. Not like Jerry Bobby or Phil could sing either :-)

"Modern PAs can self-tune the whole system just from playing a short burst of white noise through the system, and listening for the response"

A technology which was developed by/with the Grateful Dead, by the way.

From what I understand they essentially financed the modern PA industry by spending a ridiculous amount of money on sound equipment. People don't realize how much money they made - they were pretty much the top grossing tour band for about 15-20 years, playing about 90-100 shows a year. And they could (and did) use those shows to experiment with sound in a way that probably no other band has done since.

I haven't watched any D&C shows, but I expect their sound quality was just as good, if not better, than the Dead's.

From one of the dead's main sound engineers, Dan Healy, who helped establish this technology (I wasn't able to find any further discussions, but I know I've read a few interviews where he talked about doing this at the soundboard).

"""What tools do modern sound engineers have at their disposal that you didn’t? Computers and all the things that became possible at the advent of computers. It’s removed the limitations to creativity. Nowadays, in terms of concert sound, you can not only correct the sound for any room, you can ongoingly correct it in real time as the room changes and as the temperature changes and as the humidity changes. We used to do that in the ’80s and ’90s – I had a complete weather station at my mix board and we tracked temperature, humidity, barometric pressure, because they change sound dispersion, sound quality. We corrected the systems accordingly. We did long, long studies and mapped it out, and we had curves so we could predict where the sound was going. We had to do that by hand. Nowadays, it happens all by itself."""

> It was totally impractical to tour with and they lost money doing so.

The whole system travelled in two articulated lorries; but it took so long to set up that eventually they used four lorries, and two systems. One set would be for tonight's gig, the other would be on the road to tomorrow's gig, or starting to set up.

I think the mikes for the vocals were three mikes, not two (you can see triple mikes in The Grateful Dead Movie). I can't remember the rationale for using three mikes. The movie also shows the WoS being set up, under the direction of Ramrod, with Garcia gently urging him to get the speaker stacks hauled up higher, because that would be "really cool".

The problem wasn’t so much the raw amount of gear, is that it was bunch of small components that weren’t particularly well integrated. A lot cabling to run every night, etc. They had to more than doh le the size of their crew, Which was the biggest expense.

The reason for three mics when filming might have been this: Two for the PA, and one for recording.

It's still very common to use largely-separate signal chains for the PA, and for recording (and/or broadcast). These days we often do it with analog or digital splits, but analog splits can [still] be problematic and digital splits didn't exist yet back then.

Analog splits might have been particularly problematic when the source is two microphones fighting eachother. And it's often [still] the case that a microphone that works well for PA is not a microphone that is ideal for non-PA use.

(Sure, we like to think of live recordings or broadcasts as being "being there," but that's almost never actually the case. When recording and/or broadcast is involved, those things are often handled as separately as is practical -- often with gear and engineers that are outside of the walls of the venue.

This allows the FOH folks to get it sounding good in the room, the recording folks to get it sounding good on tape/DAW, and the broadcast folks to get it sounding good on radio/TV. They're different goals, and they've each got different approaches.)

This is very similar to how noise cancellation works on cell phones. The secondary mic is typically on the back of the phone and picks up the ambient noise to be subtracted from the primary mic’s signal.

Since balanced cables predate the GD, this strikes me as an acoustic implementation of an EE concept. Neat!

Here's a fun one. I'm involved in maintaining the audio system for an auditorium used by a non-profit. After a flood and remodel, including replacing some audio components (like microphones), it was observed that the microphone on the main podium always had a 60 Hz hum. The hum depended on where the microphone was facing. Sometimes it was there, sometimes it was not.

Being a non-profit facility, there are no fancy DSPs to notch out the hum or anything like that, so more creative solutions were investigated. It was determined through dumb experimentation that orienting an identical microphone 180 degrees to the one with the hum and setting the gain similarly would nearly eliminate the hum.

Eventually, the working theory became that a relatively new large pad transformer installed across the street was being picked up by the microphones. Orienting one microphone 180 degrees from the other caused the hum to be picked up out of phase from the main, and thus could be mixed in to cancel out the main mic hum.

Ultimately the real solution was simply buying better microphones, but there was a period of some months while a microphone sat off stage, pointed backwards.

It's been quite a few years since I last worked in live show production, but on any show at a venue where we couldn't be sure of access to clean power, humbuckers (not the guitar pickups, a nickname for what I believe was just a dumb 60hz notch filter or ground loop isolator inlined on house power taps) were a standard pack out in the road kit.

I would have expected that this decades-old and well established component of power infrastructure would have been commoditized by now and integrated into any dedicated AV performance/production space such as an auditorium.

Nonprofit and church auditoriums and halls are often about fifty years out of date and are somewhat around “barely working”.

I can confirm this from experience. In addition if there are any professional sound engineers involved it's likely a coincidence due to lack of funding.

> what I believe was just a dumb 60hz notch filter

A simple notch filter won't fix 60 Hz hum. Or, at least, when I've tried to eliminate annoying 60 Hz hum in my own amateur recordings, it's never been very effective. The problem is that the 60 Hz hum isn't a sine wave. It's more like a square, so you've got a bunch of harmonics up the frequency spectrum to worry about too. You can try to also notch out 120, 180, 240, etc. but it starts to get weird sounding fast.

That is my kind of tickler/teaser. Thanks for the share.

With the orchestra spread out on stage from left to right, and a bi-directional mic overhead with the capsule facing left-right, you get a channel which is largely the difference between what a listener at the same position would be hearing from each ear. Not exactly, but something like that. So not very listenable on its own.

On the same pole facing down at the entire band, you have the omnidirectional mic trying to capture the whole thing as good as possible, suitable for live broadcast from this other channel alone. They didn't have stereo radio yet anyway.

Afterward back in the studio, starting with only the two channels on reel-to-reel tape, the "difference" channel can be phase-inverted to an auxiliary tape, then you have three channels suitable for mixing.

And with analog techniques like this they can be mixed "down" to 5.1 surround sound.

From a single mic stand and only two live signals.

I have a pair of cardioid Neumann sdc that I usually use for a similar purpose, set with on a dual mount with capsules 180° opposed outward.

The history of balanced lines (common mode rejection, differential pair, etc.) is fascinating. Apparently the first twists (as in "twisted pair" to pick up external interference as similarly as possible on each conductor) were achieved not within a bundled cable, but between utility poles. Every two spans would constitute a full twist, with two single wires alternating from left to right on the cross member.

But as for the acoustic implementation, even that has a long history. The Dead borrowed the idea from fighter pilot headsets, the only difference being that pilots were contending with a noisy cockpit rather than feedback. Same general idea that the unwanted sound hits both mics somewhat equally while the voice hits both mics somewhat unequally.

The cable pairs within an ethernet cable have different twist rates, to reduce crosstalk.

On some ethernet cables.

Therein lies the difference between Cat5 and Cat5e: Cat5 pairs were all twisted at the same frequency, while Cat5e pairs must not be twisted at the same frequency.

(This is also how we were able to transition so quickly and cheaply from Cat5 to Cat5e: All that was needed to produce Cat5e on a line that had been producing Cat5 was just a relative speed change on the machines that twisted up the individual pairs.)

This goes WAY back to long-run trunked telegraph cables. They would use different twist rates and handedness as well.

> common signal in both (i.e. the sound coming out of the speakers) is nulled out, but the difference signal (the voice) makes it through.

What drives this? Singers and speakers are both localized sources, so I'd expect the mics to pick up similar phases for each.

I bet it's distance! Falloff depends on distance to source, so there should be a larger difference in volume for closer sources.

Yeah one microphone was behind the other, though I was under the impression it was half a wavelength behind and thus created something quite akin to modern active noise-cancellation?

Edit: Apparently this is not the case!

A very literal phased array!

When I saw them (back in 83, it's been a long strange trip) it looked more like one mic was on top of the other with about a 6 inch separation.

See https://archive.org/post/256492/the-betty-question-answered for more details both on WoS and the microphone setup.

Half wave length in what frequency would be the first thing that would give me pause to this. I'm reading this after your edit, but even before I got to the edit my brain was already heading towards nope

Yeah that asterisk popping up in my head was why I did some more digging as well :) thought tbf, the Dead never seemed to care much about vocal quality so it wouldn’t have been crazy for this to work well only for a narrow band. I don’t have any intuition for exactly how narrow that band would be and how that’d sound in practice though.

Yep, you sing into one but not the other, so there's a big difference in the vocal signal, whereas spill from the speakers is going to hit both mics pretty well evenly.

Here is a much more detailed article that covers the mics and so much more: https://www.vice.com/en/article/wnnayb/the-wall-of-sound

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