Reprocessed Stereo (with example)
 

During the early1970's the major UK record
companies decided that mono LPs would be
discontinued. However there was still
a very large back catalogue in mono - fine
recordings of excellent performances - for
which there was still a considerable demand.

There had been many efforts to produce
"electronic stereo" by means of EQ and
pan pots in an attempt to "separate"
instruments into frequency bands and pan
them across the stereo spectrum, left to right.
Most of these sounded awful.

At the studio were I worked, a small group
of us discussed an idea to create electronic
stereo soundstage using phase/time shift,
rather than treat the recording itself with
equalisation. Our aim, was to simulate a
recording made with a co-incidental pair
of microphones.

The brief from our production team was to
provide a stereo master which, with both
channels summed (i.e played mono), would
be indistinguishable from the original mono,
with no degradation of the original sound.

This clearly tagged the EQ method as a
complete non-starter.

This was long before the days of digital
processors and computer plug-ins, so
we resorted to three Studer analogue tape
machines - a C37 mono full-track quarter-inch
source machine, an eight track A80 running at 30 ips
with Doldy "A" and a stereo A80 quarter-inch
15ips master recorder with Dolby "A"

The idea, simple in itself, depended on the delay
between the record and playback head on the
multitrack machine to introduce a sense of width
in the sound stage..

To set the delay, a VCSC (variable capstan speed
control) was used on the high-speed multitrack machine.
The audio from the mono source was sent to two tracks
of the multitrack, with the phase of the second track
reversed, so that when they were brought back from
the replay chain to the console, they had 180 degree
phase difference, and cancelled out when switched mono.

Having established the required delay, which was
dependent on both the music content and the location
in which it had been recorded, one could set up
the "stereo sound stage" by bringing up the
original mono signal on the mixing desk, and then
adding to it the out-of-phase pair, at some 10dB
below the mono signal.

We demonstrated the idea by first playing the
"stereo" tape with both tracks panned centre
for mono, and then after about one minute,
opening the pans to L and R. Listeners
were impressed. We wanted to avoid the
word "electronic" and so called it
"reprocessed stereo"

A large number of early classical recordings
were reprocessed using this system for our own
label and also for third party labels. The compatibility
test was perfect, and switching to stereo gave a
spread to the original recording with no other changes.

Here is one of my experiments with a jazz track.

On this audio extract, there are three segments.
The first is mono, the second is reprocessed stereo,
and the third segment is a good example of what happens
when the level difference of mono signal and the
out-of-phase pair is too small.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3


Iain

Reprocessed Stereo (with example)
 

On Thu, 19 Jan 2017 14:45:47 +0200, "Iain Churches"
wrote:

During the early1970's the major UK record
companies decided that mono LPs would be
discontinued. However there was still
a very large back catalogue in mono - fine
recordings of excellent performances - for
which there was still a considerable demand.

There had been many efforts to produce
"electronic stereo" by means of EQ and
pan pots in an attempt to "separate"
instruments into frequency bands and pan
them across the stereo spectrum, left to right.
Most of these sounded awful.

At the studio were I worked, a small group
of us discussed an idea to create electronic
stereo soundstage using phase/time shift,
rather than treat the recording itself with
equalisation. Our aim, was to simulate a
recording made with a co-incidental pair
of microphones.

The brief from our production team was to
provide a stereo master which, with both
channels summed (i.e played mono), would
be indistinguishable from the original mono,
with no degradation of the original sound.

This clearly tagged the EQ method as a
complete non-starter.

This was long before the days of digital
processors and computer plug-ins, so
we resorted to three Studer analogue tape
machines - a C37 mono full-track quarter-inch
source machine, an eight track A80 running at 30 ips
with Doldy "A" and a stereo A80 quarter-inch
15ips master recorder with Dolby "A"

The idea, simple in itself, depended on the delay
between the record and playback head on the
multitrack machine to introduce a sense of width
in the sound stage..

To set the delay, a VCSC (variable capstan speed
control) was used on the high-speed multitrack machine.
The audio from the mono source was sent to two tracks
of the multitrack, with the phase of the second track
reversed, so that when they were brought back from
the replay chain to the console, they had 180 degree
phase difference, and cancelled out when switched mono.

Having established the required delay, which was
dependent on both the music content and the location
in which it had been recorded, one could set up
the "stereo sound stage" by bringing up the
original mono signal on the mixing desk, and then
adding to it the out-of-phase pair, at some 10dB
below the mono signal.

We demonstrated the idea by first playing the
"stereo" tape with both tracks panned centre
for mono, and then after about one minute,
opening the pans to L and R. Listeners
were impressed. We wanted to avoid the
word "electronic" and so called it
"reprocessed stereo"

A large number of early classical recordings
were reprocessed using this system for our own
label and also for third party labels. The compatibility
test was perfect, and switching to stereo gave a
spread to the original recording with no other changes.

Here is one of my experiments with a jazz track.

On this audio extract, there are three segments.
The first is mono, the second is reprocessed stereo,
and the third segment is a good example of what happens
when the level difference of mono signal and the
out-of-phase pair is too small.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3


Iain


Mono for me. The second segment still has everything I want to hear at
centre front, but with some vague "stuff" round the sides. The third
part sounds like someone has got the phasing totally wrong somewhere
down the line.

d

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Reprocessed Stereo (with example)
 

On 19/01/2017 12:45, Iain Churches wrote:
During the early1970's the major UK record
companies decided that mono LPs would be
discontinued. However there was still
a very large back catalogue in mono - fine
recordings of excellent performances - for
which there was still a considerable demand.

There had been many efforts to produce
"electronic stereo" by means of EQ and
pan pots in an attempt to "separate"
instruments into frequency bands and pan
them across the stereo spectrum, left to right.
Most of these sounded awful.

At the studio were I worked, a small group
of us discussed an idea to create electronic
stereo soundstage using phase/time shift,
rather than treat the recording itself with
equalisation. Our aim, was to simulate a
recording made with a co-incidental pair
of microphones.

The brief from our production team was to
provide a stereo master which, with both
channels summed (i.e played mono), would
be indistinguishable from the original mono,
with no degradation of the original sound.

This clearly tagged the EQ method as a
complete non-starter.

This was long before the days of digital
processors and computer plug-ins, so
we resorted to three Studer analogue tape
machines - a C37 mono full-track quarter-inch
source machine, an eight track A80 running at 30 ips
with Doldy "A" and a stereo A80 quarter-inch
15ips master recorder with Dolby "A"

The idea, simple in itself, depended on the delay
between the record and playback head on the
multitrack machine to introduce a sense of width
in the sound stage..

To set the delay, a VCSC (variable capstan speed
control) was used on the high-speed multitrack machine.
The audio from the mono source was sent to two tracks
of the multitrack, with the phase of the second track
reversed, so that when they were brought back from
the replay chain to the console, they had 180 degree
phase difference, and cancelled out when switched mono.

Having established the required delay, which was
dependent on both the music content and the location
in which it had been recorded, one could set up
the "stereo sound stage" by bringing up the
original mono signal on the mixing desk, and then
adding to it the out-of-phase pair, at some 10dB
below the mono signal.

We demonstrated the idea by first playing the
"stereo" tape with both tracks panned centre
for mono, and then after about one minute,
opening the pans to L and R. Listeners
were impressed. We wanted to avoid the
word "electronic" and so called it
"reprocessed stereo"

A large number of early classical recordings
were reprocessed using this system for our own
label and also for third party labels. The compatibility
test was perfect, and switching to stereo gave a
spread to the original recording with no other changes.


Many years ago I built a gadget to do the same thing with an op-amp, 3
resistors and a capacitor.
Constant amplitude with a delay at higher frequencies on one channel.
It worked OK but there was no point - mono doesn't sound any better when
spread thinly.

--
Eiron.

Reprocessed Stereo (with example)
 

"Eiron" wrote in message
...

Many years ago I built a gadget to do the same thing with an op-amp, 3
resistors and a capacitor.
Constant amplitude with a delay at higher frequencies on one channel.

Interesting. Was this totally mono compatible with the original?
That was the main part of the brief.

Iain

Reprocessed Stereo (with example)
 

"Don Pearce" wrote in message
...
On this audio extract, there are three segments.
The first is mono, the second is reprocessed stereo,
and the third segment is a good example of what happens
when the level difference of mono signal and the
out-of-phase pair is too small.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3

Mono for me.

For me too. But when the people upstairs decide there will be
no more mono, there will be no more mono. Fortunately, these
days we are more enlightened, and listeners expect mono archive
material to be preserved in pristine mono.

The second segment still has everything I want to hear at
centre front, but with some vague "stuff" round the sides.

Frequency analysis of the original mono, and the reprocessed stereo
track:

Mono
http://www.kolumbus.fi/iain.churches...requency01.png

Reprocessed Stereo
http://www.kolumbus.fi/iain.churches...requency02.png

Phase analysis

Mono
http://www.kolumbus.fi/iain.churches.../ESPhase01.png

Reprocessed stereo
http://www.kolumbus.fi/iain.churches.../ESPhase02.png

The third
part sounds like someone has got the phasing totally wrong somewhere
down the line.

Your analysis of the third segment was spot on, Don,
and illustrates well the importance of the relationship
of the mono centre signal to the out of phase pair.

"Overcooked"
http://www.kolumbus.fi/iain.churches.../ESPhase03.png

Iain






d


http://www.kolumbus.fi/iain.churches...requency01.png

Reprocessed Stereo (with example)
 

On 19/01/2017 14:54, Iain Churches wrote:
"Eiron" wrote in message
...

Many years ago I built a gadget to do the same thing with an op-amp, 3
resistors and a capacitor.
Constant amplitude with a delay at higher frequencies on one channel.

Interesting. Was this totally mono compatible with the original?
That was the main part of the brief.

No but that wasn't necessary as my gadget was part of the replay chain
and could have been fitted into an amp (instead of a tobacco tin) with
a defeat switch and a pot for 'image width'.

I didn't think of using my tape deck as a delay.

--
Eiron.

Reprocessed Stereo (with example)
 

"Eiron" wrote in message
...
On 19/01/2017 14:54, Iain Churches wrote:
"Eiron" wrote in message
...

Many years ago I built a gadget to do the same thing with an op-amp, 3
resistors and a capacitor.
Constant amplitude with a delay at higher frequencies on one channel.

Interesting. Was this totally mono compatible with the original?
That was the main part of the brief.

No but that wasn't necessary as my gadget was part of the replay chain
and could have been fitted into an amp (instead of a tobacco tin) with
a defeat switch and a pot for 'image width'.

I didn't think of using my tape deck as a delay.

Tape decks we had plenty of:-)

The Studer with external capstan control, was running
well in excess of 30 ips.

At one stage we tried, in addition to the main antiphase
pair, three pairs lightly EQ'd. These were added sparingly,
as one might add condiments in cooking! Once again in
mono, these pairs too cancelled out, just leaving a track
indistinguishable from the mono original.

Generally speaking the reprocessed material that I was
involved with was jazz and classical.

Iain

Reprocessed Stereo (with example)
 

Iain Churches wrote:


During the early1970's the major UK record
companies decided that mono LPs would be
discontinued. However there was still
a very large back catalogue in mono - fine
recordings of excellent performances - for
which there was still a considerable demand.

There had been many efforts to produce
"electronic stereo" by means of EQ and
pan pots in an attempt to "separate"
instruments into frequency bands and pan
them across the stereo spectrum, left to right.
Most of these sounded awful.

At the studio were I worked, a small group
of us discussed an idea to create electronic
stereo soundstage using phase/time shift,
rather than treat the recording itself with
equalisation. Our aim, was to simulate a
recording made with a co-incidental pair
of microphones.

The brief from our production team was to
provide a stereo master which, with both
channels summed (i.e played mono), would
be indistinguishable from the original mono,
with no degradation of the original sound.

This clearly tagged the EQ method as a
complete non-starter.

This was long before the days of digital
processors and computer plug-ins, so
we resorted to three Studer analogue tape
machines - a C37 mono full-track quarter-inch
source machine, an eight track A80 running at 30 ips
with Doldy "A" and a stereo A80 quarter-inch
15ips master recorder with Dolby "A"

The idea, simple in itself, depended on the delay
between the record and playback head on the
multitrack machine to introduce a sense of width
in the sound stage..

To set the delay, a VCSC (variable capstan speed
control) was used on the high-speed multitrack machine.
The audio from the mono source was sent to two tracks
of the multitrack, with the phase of the second track
reversed, so that when they were brought back from
the replay chain to the console, they had 180 degree
phase difference, and cancelled out when switched mono.

Having established the required delay, which was
dependent on both the music content and the location
in which it had been recorded, one could set up
the "stereo sound stage" by bringing up the
original mono signal on the mixing desk, and then
adding to it the out-of-phase pair, at some 10dB
below the mono signal.

We demonstrated the idea by first playing the
"stereo" tape with both tracks panned centre
for mono, and then after about one minute,
opening the pans to L and R. Listeners
were impressed. We wanted to avoid the
word "electronic" and so called it
"reprocessed stereo"

A large number of early classical recordings
were reprocessed using this system for our own
label and also for third party labels. The compatibility
test was perfect, and switching to stereo gave a
spread to the original recording with no other changes.

Here is one of my experiments with a jazz track.

On this audio extract, there are three segments.
The first is mono, the second is reprocessed stereo,
and the third segment is a good example of what happens
when the level difference of mono signal and the
out-of-phase pair is too small.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3



** Listening on headphones while operating the "stereo-mono"
switch on my amp:

Segment 1 is plain mono.

Segment 2 has some ambience coming from L & R of center -
which disappears entirely when switched to mono.

Segment 3 in simply out of phase - the level drops by over
15db when switched to mono leaving mostly swishy sounding
artefacts from the low bit rate MP3.

In fact, I hear swishy cymbals on all three segments.

I think a similar trick was once used with stereo recordings
to create signals for rear speakers - using a BBD delay and
reverse phase.



.... Phil

Reprocessed Stereo (with example)
 

"Phil Allison" wrote in message
...

** Listening on headphones while operating the "stereo-mono"
switch on my amp:

Segment 1 is plain mono.

Yes.

Segment 2 has some ambience coming from L & R of center -
which disappears entirely when switched to mono.

That was the producers' brief, total mono compatibility with
no change in the original sound.

Segment 3 in simply out of phase - the level drops by over
15db

Yes. It was done to illustrate the importance of the ratio
of centre to side signals. Normally the centre signal needs to
be some 6 to 10dB stronger. In segment 3 the levels are
equal.

In fact, I hear swishy cymbals on all three segments.

That's probably due to the low res of the track which I
posted.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3


Iain

Reprocessed Stereo (with example)
 

Yes I experimented with this sort of thing domestically around that time.
However a huge number of mono recordings by emi and Deca and polydor were
made using delays and naff frequency shifts that all sounded like you had a
bad head cold in stereo or like it was being played in a subway in mono.
The best effect i had was with small amounts of reverb, but different on
each track. Sadly though the mono in such cases did not sound like normal
mono as there were frequencies where the differing reverb cancelled and gave
the impression of notch filtering.


One of the worst recent examples of attempting to do stereo was rather
ominously called the very worst of Spike Jones.
The content was as witty and daft as expected but spot effects massively
filtered pan potted all over the place was completely ridiculous.
Brian

--
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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Iain Churches" wrote in message
...
During the early1970's the major UK record
companies decided that mono LPs would be
discontinued. However there was still
a very large back catalogue in mono - fine
recordings of excellent performances - for
which there was still a considerable demand.

There had been many efforts to produce
"electronic stereo" by means of EQ and
pan pots in an attempt to "separate"
instruments into frequency bands and pan
them across the stereo spectrum, left to right.
Most of these sounded awful.

At the studio were I worked, a small group
of us discussed an idea to create electronic
stereo soundstage using phase/time shift,
rather than treat the recording itself with
equalisation. Our aim, was to simulate a
recording made with a co-incidental pair
of microphones.

The brief from our production team was to
provide a stereo master which, with both
channels summed (i.e played mono), would
be indistinguishable from the original mono,
with no degradation of the original sound.

This clearly tagged the EQ method as a
complete non-starter.

This was long before the days of digital
processors and computer plug-ins, so
we resorted to three Studer analogue tape
machines - a C37 mono full-track quarter-inch
source machine, an eight track A80 running at 30 ips
with Doldy "A" and a stereo A80 quarter-inch
15ips master recorder with Dolby "A"

The idea, simple in itself, depended on the delay
between the record and playback head on the
multitrack machine to introduce a sense of width
in the sound stage..

To set the delay, a VCSC (variable capstan speed
control) was used on the high-speed multitrack machine.
The audio from the mono source was sent to two tracks
of the multitrack, with the phase of the second track
reversed, so that when they were brought back from
the replay chain to the console, they had 180 degree
phase difference, and cancelled out when switched mono.

Having established the required delay, which was
dependent on both the music content and the location
in which it had been recorded, one could set up
the "stereo sound stage" by bringing up the
original mono signal on the mixing desk, and then
adding to it the out-of-phase pair, at some 10dB
below the mono signal.

We demonstrated the idea by first playing the
"stereo" tape with both tracks panned centre
for mono, and then after about one minute,
opening the pans to L and R. Listeners
were impressed. We wanted to avoid the
word "electronic" and so called it
"reprocessed stereo"

A large number of early classical recordings
were reprocessed using this system for our own
label and also for third party labels. The compatibility
test was perfect, and switching to stereo gave a
spread to the original recording with no other changes.

Here is one of my experiments with a jazz track.

On this audio extract, there are three segments.
The first is mono, the second is reprocessed stereo,
and the third segment is a good example of what happens
when the level difference of mono signal and the
out-of-phase pair is too small.

http://www.kolumbus.fi/iain.churches...StereoDemo.mp3


Iain