Novice questions re: mono/stereo/multitrack

[2Jiggery]

Hi, I’m a newbie on this forum, so apologies if I have not posted this in the correct place.

I am attempting to educate myself re: the fundamentals of recording, and I have a few very basic questions. I have searched for answers online, but am struggling to understand a couple of basic concepts. If anyone can help it would be much appreciated.

Firstly, my questions are related to mono/stereo/multitrack recording.
Re: ‘2 track’ recording. I understand that mono is mono, and historically 2 track refers to stereo, correct? And then there is multi-track recording, eg 4 track. But therefore my question is, surely 2 track is multitrack? If there are 2 tracks then surely you could record 1 mono instrument simultaneously with another, rather than using both tracks for stereo purposes? Surely anything more than 1 track is multitrack?
I realise the question is probably fundamentally flawed, but what am I not understanding here?

And a further question re: mono and stereo. I understand that the Beatles recorded the majority of their albums in mono. (although I also understand that all of their earlier albums were released in both mono and stereo, with George Martin and the engineers doing a stereo mix after the Beatles mixed them in mono).
But 'abbey road' was recorded in stereo. In practical terms, what does 'recorded in stereo' mean? What was done differently to their previous albums? Eg did they suddenly use 2 mics and 2 channels on the vocals/guitar amp etc, where previously there would only have been one? Or was it just that they were now involved in the stereo mixing process? Or was the desk that they used 'stereo', whereas previously it had only been mono?
Again, I appreciate that I may be asking the wrong question...

Many thanks in advance!

[Sam Spoons]

Hi and welcome to the forum

Some two track recorders can record each track separately but most can't so can only be used for recording two tracks simultaneously and are usually used to make a stereo recording. Machines commonly referred to as 'multitrack' can usually record each track singly while playing back previously recorded tracks for the performer to play along to. They have anything from 4 tracks up to, typically, 24 for hardware recorders, computer based recording systems can have virtually unlimited tracks.

The Beatles recorded initially using 'Sound on Sound'* (see what I did there?) where a group of instruments were recorded onto one tape machine then that tape was played back while the band played additional instruments and/or sang while a mix of the two was recorded on a second tape machine, then this could be repeated. The problem was that this severely limited the options for mixing afterwards and it was only when the early multitrack recorders came along that any significant mixdown could take place. The whole history is well documented so I won't attempt to go further except to say that I guess the mono/stereo thing was considered a bit of a gimmick to start with and I remember 'stereo' records with the drums and instruments on one side with vocals and, maybe a lead/solo instrument on the other (sounds totally weird to modern ears, actually it did then too...).

Abbey Rd was recorded on 8 track recorders which allowed enough tracks to plan where each instrument would end up in the stereo soundscape, something that 4 tracks didn't really allow. That said 'Sound on Sound' techniques would still have been used to allow all the extra instruments.

* I don't know if the Beatles' very first recordings were 'one take into a mono recorder but I suspect they may have been.

edit :- Wikipedia has pretty comprehensive explanations of the techniques used on The Beatles recordings including some detail on how they achieved stereo from multiple 4 track machines.

[2Jiggery]

Hi Sam,

Many thanks for this detailed reply.

That's very helpful info regarding 2 track recording (perhaps I should have specified that I was asking purely about analog, but obviously you got that!). So if I understand correctly, historically 2 track is not associated with multi-tracking, even though some machines were capable of it? And therefore, 2 track usually just refers to stereo?

Thanks also for the info regarding the Beatles recordings. Yes that makes sense, if they used an 8track recorder where previously they had used 4track. Presumably that was the big difference in making the switch to stereo recording?

Thanks again, much appreciated.

[Sam Spoons]

Strictly 2 track can be used to reproduce either two discreet tracks or one stereo track. A '2 track master' would almost certainly be stereo.

WRT The Beatles and their mono and stereo dilemma have a think about how you could record, say, 8 instruments using only 4 track tape machines then, if you don't already understand the principle*, do a search for 'bouncing' and see how limiting it could be compared to having more tracks available.

* Sorry if I'm teaching you to 'suck eggs' here

edit :- the pencil icon at the top right is the edit button. You have IIRC 45 mins from first posting then it disappears.

edit 2 :- Oh you've found it...

[2Jiggery]

Not at all, this is exactly the info I'm after.

I understand the principles of multi-tracking and bouncing, but hadn't really considered how a 4 track wouldn't really give "enough tracks to plan where each instrument would end up in the stereo soundscape", as you explained. Hence the ability to work in stereo on an 8 track (if I've understood correctly!)

[Sam Spoons]

If you do it right 4 tracks can be surprisingly flexible, and Georg Martin and The Beatles were nothing if not inventive but maybe aiming for stereo just meant too many bounces for acceptable quality? I guess we'll never know for sure what their though processes were.. But there's lots of information out there about their methods and it's a fascinating rabbit hole to go down

[Hugh Robjohns]

the term multitrack generally denotes the ability to record separate instruments/voices on their own separate tracks. So while a two-track machine is, technically, multiple tracks there's not much you can really do with only two separate sound sources. With four track the possibilities start to open up (drum, bass, guitar, vocal, for example), and with 8, 16, 24 or 48 you can really do some interesting things!

With four track, you can have a stab at stereo mixes for very simple stuff, but once you start overdubbing so each track carries multiple instruments you're really limited to panning tracks hard left, centre or hard right... which can work, but more individual tracks allows for more individual panning options and is thus far more flexible.

[2Jiggery]

Useful to have this clarified, many thanks.

[Tomás Mulcahy]

Actually the Beatles did use 2 track, so they could concentrate on playing the music and then overdub the vocals. Standard procedure for pop production at EMI at the time. EMI's BTR3 stereo machine was specifically designed for this purpose. The 2 track head had a bigger gap than the stereo recording head, to prevent feedback when monitoring channel 1 during the overdub. The dedicated record and replay electronics were in six (I think) discrete sections making it possible to overdub in sync. And made the machine bigger than your fridge! Apparently it was initially designed to support 4 track recording, but the prototype was rejected.

You can hear it for yourself in the "stereo" mix of With the Beatles. The vocals are on the right. If you isolate the right side you can hear that they used a speaker, not headphones, as the monitor. The used a figure of 8 mic with the speaker in the null, so you hear nice room ambience on the right, and the chamber return is clearly audible over the music on the left. Technology moved on to headphones for monitoring and the Telefunken then the more famous Studer 4 tracks.

This is documented in the book Recording the Beatles. Unfortunately I no longer own a copy so this is all from memory.

[Hugh Robjohns]

... EMI's BTR3 stereo machine was specifically designed for this purpose. The 2 track head had a bigger gap than the stereo recording head, to prevent feedback when monitoring channel 1 during the overdub.

I presume you mean the guard band (between the two tracks) was wider on the two-track record head than that in the equivalent stereo record head track? Obviously, a smaller guard band means a greater area of magnetised tape and thus a lower noise floor, so a narrow guard band is preferable from a noise point of view... but if adjacent tracks are carrying unrelated material unwanted magnetic crosstalk between channels (either on the tape or in the head windings) can indeed be problematic. So machines designed specifically for recording different and unrelated material on adjacent tracks do generally have wider guard bands.

The 'gap' in a tape head context usually refers to the opening in the pole piece which generates the external magnetic field. In the replay head, the gap has to be as narrow as possible to maximise the high frequency response (a large gap has a low 'extinction frequency' where the response rolls off rapidly due to the recorded signal wavelength approaching the gap dimension).

The dedicated record and replay electronics were in six (I think) discrete sections making it possible to overdub in sync.

The only requirement for overdubbing in sync is being able to replay from the non-recording channel of the record head, while simultaneously recording through the other channel -- thus ensuring that what you hear and what you overdub are in sync on the tape.

However, a bespoke record head normally has a much wider gap than a dedicated replay head as it is designed and optimised to perform a different function. Consequently, when used for sync replay the record head output has a significantly different frequency response and sensitivity compared to the dedicated replay head.

So the reference to six separate electronics sections probably refers to channel 1 and 2 record amplifiers, channel 1 and 2 replay head amplifiers, and channel 1 and 2 record head sync-replay amplifiers. For sync overdubbing the relevant replay channel of the record head is switched away from the record amp and into the corresponding sync replay amplifier which is tuned to extract the best possible quality... But full quality replay for mixing etc would be performed via the dedicated replay head and replay amplifiers. Of course, other electronics sections would be needed for the bias and erase head amplifiers, and in later machines if not the BTR3 for the transport motor controls.

This six-amp idea persisted right to the end of the tape recorder era. For example, I have a Revox PR99 which has separate replay and sync-replay amplifiers, plus record amplifiers, all on separate cards mounted in separate slots in a card frame at the bottom of the machine.

I've only seen pictures of BTR3s, but I did lay hands on a few BTR2s in my BBC days -- not in live broadcasting channels I'm relieved to say, but at the training centre where a few were retained. Huge clunking green things...

[2Jiggery]

Actually the Beatles did use 2 track, so they could concentrate on playing the music and then overdub the vocals. Standard procedure for pop production at EMI at the time. EMI's BTR3 stereo machine was specifically designed for this purpose. The 2 track head had a bigger gap than the stereo recording head, to prevent feedback when monitoring channel 1 during the overdub. The dedicated record and replay electronics were in six (I think) discrete sections making it possible to overdub in sync. And made the machine bigger than your fridge! Apparently it was initially designed to support 4 track recording, but the prototype was rejected.

You can hear it for yourself in the "stereo" mix of With the Beatles. The vocals are on the right. If you isolate the right side you can hear that they used a speaker, not headphones, as the monitor. The used a figure of 8 mic with the speaker in the null, so you hear nice room ambience on the right, and the chamber return is clearly audible over the music on the left. Technology moved on to headphones for monitoring and the Telefunken then the more famous Studer 4 tracks.

This is documented in the book Recording the Beatles. Unfortunately I no longer own a copy so this is all from memory.

Funnily enough I came across that book on my searches yesterday. And at a cursory glance the cheapest copy I could find was £500!

The pictures of the BTR3 are fantastic. What a piece of gear. There's a thing on YouTube where someone has a BTR2/3. Wonderful stuff.

I just listened to some of With the Beatles with the right side isolated. Incredible to hear the speaker in the room so clearly behind the vocals. Thanks for this, it's so cool to get inside the recordings.

[2Jiggery]

... EMI's BTR3 stereo machine was specifically designed for this purpose. The 2 track head had a bigger gap than the stereo recording head, to prevent feedback when monitoring channel 1 during the overdub.

I presume you mean the guard band (between the two tracks) was wider on the two-track record head than that in the equivalent stereo record head track? Obviously, a smaller guard band means a greater area of magnetised tape and thus a lower noise floor, so a narrow guard band is preferable from a noise point of view... but if adjacent tracks are carrying unrelated material unwanted magnetic crosstalk between channels (either on the tape or in the head windings) can indeed be problematic. So machines designed specifically for recording different and unrelated material on adjacent tracks do generally have wider guard bands.

The 'gap' in a tape head context usually refers to the opening in the pole piece which generates the external magnetic field. In the replay head, the gap has to be as narrow as possible to maximise the high frequency response (a large gap has a low 'extinction frequency' where the response rolls off rapidly due to the recorded signal wavelength approaching the gap dimension).

The dedicated record and replay electronics were in six (I think) discrete sections making it possible to overdub in sync.

The only requirement for overdubbing in sync is being able to replay from the non-recording channel of the record head, while simultaneously recording through the other channel -- thus ensuring that what you hear and what you overdub are in sync on the tape.

However, a bespoke record head normally has a much wider gap than a dedicated replay head as it is designed and optimised to perform a different function. Consequently, when used for sync replay the record head output has a significantly different frequency response and sensitivity compared to the dedicated replay head.

So the reference to six separate electronics sections probably refers to channel 1 and 2 record amplifiers, channel 1 and 2 replay head amplifiers, and channel 1 and 2 record head sync-replay amplifiers. For sync overdubbing the relevant replay channel of the record head is switched away from the record amp and into the corresponding sync replay amplifier which is tuned to extract the best possible quality... But full quality replay for mixing etc would be performed via the dedicated replay head and replay amplifiers. Of course, other electronics sections would be needed for the bias and erase head amplifiers, and in later machines if not the BTR3 for the transport motor controls.

This six-amp idea persisted right to the end of the tape recorder era. For example, I have a Revox PR99 which has separate replay and sync-replay amplifiers, plus record amplifiers, all on separate cards mounted in separate slots in a card frame at the bottom of the machine.

I've only seen pictures of BTR3s, but I did lay hands on a few BTR2s in my BBC days -- not in live broadcasting channels I'm relieved to say, but at the training centre where a few were retained. Huge clunking green things...

That's some serious knowledge (which I hope to understand one day! although I realise it was more intended for the previous poster). Very impressed that you've actually used some of these machines though.

[Tomás Mulcahy]

Thanks Hugh, all memory gaps filled