Recording - September 2016 - 61

below 600 Hz and above 10 kHz. Thus the reverb on Beatles
recordings has a characteristic sound-it's all essentially
midrange. Since the majority of vocal sound lies in the midrange,
and since the chamber was used most often on vocals, many
Beatles vocals (especially on their earlier recordings) have that
characteristic midrangey sound. Now you know.
Well, you're not going to build a whopping big chamber
inside or behind your house, but as I mentioned, digital simulations have gotten very good.
Slap me back
In the 1950s, the engineers who ran the small studios and
record companies where Rhythm & Blues and rock were being
invented didn't have the money to build big chambers. They
were mostly shoestring operations like Sam Phillips's Memphis
Recording Service/Sun Records and the Chess brothers' Chess
Records. (The engineers at Berry Gordy's Motown Records did
build a couple of chambers-but Motown was way beyond
the shoestring stage by then. See our interview with John
Windt, October 2014.)
These low-budget operators pioneered the use of a spare
tape recorder to add echo (really echo, not reverb) to recordings. They would pipe the signals on which they wanted echo
(usually vocals, sometimes guitars) to the input of that tape
recorder; the short time delay added by the time the tape took
to move from the record head to the playback head created the
delayed signal that, fed back into the console and mixed with
the dry source, produced the echo effect. The record and playback heads on a typical Ampex tape recorder were spaced
about 2.58" apart, producing a delay of 172 milliseconds (ms)

tape; all of these colorations showed up in the slap echo. Just
adding delay to a signal won't have that Fifties-funky sound-
unless you use one of the popular plug-ins that simulates a
tape recorder's timbre, which will get you pretty darn close.
Mechanical reverb I: boing and twang
Let's go back to the chamber for a minute, and look at it in
an abstract way. What the recording engineer was doing with
a chamber was introducing the dry signal into a medium in
which it could bounce back and forth and around and
around; the bounces merged with each other to create the
desired wash of reverberation.
As far back as 1939, the inventor Laurens Hammond developed a small metal box (called a reverb tank) with one or
more metal springs inside, rather like the springs on an oldfashioned screen door. A transducer rather like the moving coil
assembly of a loudspeaker, when driven by an amplifier fed a
dry signal from the recording console, set the springs to vibrating. The vibrations spread throughout the spring, and when
they reached the end, another transducer converted them back
into electrical signals, which would get fed back to the console
and added to the dry signal.
Meanwhile, the signal would boing its way back up the
spring; when it reached the beginning, it would boing back
down, continuing until internal friction within the spring
stopped the vibrations. Conceptually, this was operating in the
same way as a reverb chamber, and spring reverb units
began showing up in guitar amplifiers-you've heard one if
you've ever listened to the guitar on a Beach Boys record.
Spring reverb accessories were also marketed as accessories

Just adding delay to a signal won't have that Fifties-funky sound-
unless you use one of the popular plug-ins that simulates a tape
recorder's timbre, which will get you pretty darn close.
at the standard professional tape speed of 15 inches per second (ips). (Remember those numbers; we'll come back to them.)
The effect is called slapback echo or simply slap echo, and
you can hear classic examples on some Sun records by
Johnny Cash and Carl Perkins, on Norman Petty's recordings
of Buddy Holly, on the Beatles' "Oh, Darling", and on just
about every reggae record ever made. Slap echo adds an
amazing amount of body to vocal sounds in particular, and it's
not surprising that it became popular.
So can you recreate the sound of classic slap echo in a
DAW mix? Well, yes; if you duplicate any track you want to
add slap to, slide it 172 ms to the right in the track window,
then add it to the mix along with all your other sources, or if
you create an "effects bus" of all the sources you want to slap
and route that bus's output through a plug-in that generates
pure delay, you can get the effect of classic slap echo. Sort of.
Here's what the "sort of" is about: the tape recorders of the
1950s were not sonically transparent. A Fifties-vintage Ampex
added some coloration due to its input and output transformers, and a lot more coloration from the tape recording process
itself. There were frequency response aberrations, and there
was often distortion caused by the nonlinearity of the era's

for hi-fi sets in the 1950s, so users could, if they wished, hear
what Frank Sinatra might sound like if he sang in a cave.
Spring reverbs were also marketed to small recording studios, but they revealed their weak point pretty quickly: that
boing-boing of the spring sounded pretty cheesy even on the
best days. The engineers at AKG in Austria (and other companies) decided to make grown-up spring reverb units, and by
using multiple springs of different sizes and adding damping
to the springs (in some cases by suspending them in oil) they
were able to achieve pretty good performance, even including
controls for the degree of damping on some models. These
improved spring reverbs found a place in many small studios
in the 1970s and 1980s. (Paul Vnuk just reviewed Universal
Audio's plug-in simulating an AKG BX20 spring reverb in
Recording's December 2015 Gift Guide.)
Mechanical reverb II: on a (steel) platter
Meanwhile, the EMT company designed a reverb system that
was conceptually similar to spring reverbs, but used a different
medium. Instead of injecting vibrations into springs, they suspended a large steel plate by its corners inside a wooden box.
The plate had two transducers mounted on it. One was the
RECORDING SEPTEMBER 2016

Table of Contents for the Digital Edition of Recording - September 2016