"The Monophonic Thread"

[Craig Maier]

Recently, there has been some discussion that not enough information exists about Monophonic recording. Thus, I am starting a thread dedicated to this topic. I will start with the following:

Monophonic recording consists of a single audio track, as opposed to stereo which consists of two, or surround sound which consists of many tracks or channels. The very first audio recording, made by Thomas Edison in 1877 at Menlo Park, NJ was monophonic and made on tin foil. The recording was of Edison himself reciting the nursery rhyme "Mary had a little Lamb whose fleece was white as snow. And everywhere that Mary went, the Lamb was sure to go". As Edison later reminisced, "it was a little piece of practical poetry."

Anyway, the following is a partial listing of monophonic recording formats that followed:

Tin Foil Cylinderical demonstration recording
Wax and Amberol Cylinders
Berliner 78's
Edison Diamond Discs
45 RPM Records from circa 1949 up through circa 1965
Early LP's from 1949 through circa 1960
Early Acetates
Wire Recordings
Early Tape Recordings
Early Optical Cine (Movie) soundtracks
Early Compact Cassette Tapes
Linear Beta Video Cassette Soundtracks
Early non-Dolby VHS Video Cassette linear soundtracks

Over a period of time, I will address some of the unique characteristics of these monophic recordings and how to deal with them on todays equipment. I will begin with Reel to Reel Magnetic Tape media, which will appear as the next element of this thread. I am starting with this media because it has been a point of recent discussion here on this bbs.

ps - please chime in with your own experiences and knowledge of the topics discussed under this thread. Please do not hold back!

[Craig Maier]

Reel to Reel Full Track Monophonic Magnetic Tape Media

Magnetic tape recording was invented by the Germans in the early 1930's but initially exhibited such poor sound quality that it was only useful for voice recording. A German company named AEG Magnetophon (Magnetophone) discoverd that the addition of an AC bias signal to the baseband audio allowed very high quality recordings to be produced with magnetic tape because of the use of the entire B-H curve of the magnetic domains on the tape (previous designs used no bias at all or fixed DC bias). AC bias increased linearity and doubled the dynamic range thus decreased the audio distortion. After this discovery, this technology was put into substantial use by the German war machine during WW2. The technology came to the US from Germany right after the war but was in very limited use in the mid 1940's. Around 1947, magnetic tape media hit the public domain through numerous radio programs that were pre-recorded for later broadcast by Bing Crosby using magnetic tape.

Originally having had a paper backing, companies like 3M created mylar and other compounds which soon replaced it because of their superior durability. Most all reel to reel tapes were 1/4 inch in width and operated at speeds ranging from the following:

30 inches per second (ips)
15 ips
7.5 ips

later on came:

3.75 ips

The original track configuration was "full track monophonic". It is important to note that the best way to play a magnetic tape is on a machine capable of the original track width and configuration format. Thus, the best results for playing a full track mono tape recording from the early 1950's would be on a full track mono player. The next best thing would be to modify a modern tape deck to contain a full track playback head.

Since most of us do not have such equipment nor the inclination to modify a tape recorder to include a full track head, one must rely on what is available. The most common professional 1/4 inch tape machine operates in stereo mode in a half track configuration. Thus, playing a full track tape of this kind of machine will yield both channels to contain the same output signal, just from different portions of the tape media. Playing a full track mono tape on this type of machine will result in a transfer almost as good as if it were transferred on a full track monophonic machine. If you are transferring a full track mono tape in this manner, it is advised to transfer both tracks discretely even though the information is mono on both. Do not use a "Y" cable to sum them together before your sound card input. Later, you will be able to choose the quietest of the two channels, or choose to sum the two together in software to determine what combination results in the best signal to noise ratio.

But, it is important to note that azimuith errors in the recording or in the playback may result in a compromise in the playback of these tapes when summed to mono because of the summated phase shift effect on the final product. This results in a bump or a notch in the spectrum at higher frequencies. Since you will be tranferrring both signals to your computer hard drive, this can be determined at a later point in time.

If you do not have a professional 1/4 inch 1/2 track machine and are stuck with the most common reel to reel format which was 1/4 inch 1/4 track stereo (staggered track configuration), despair not. You can still play your old full track mono tapes with reasonable results, just not optimum. You will find that the mono signal shows up on both output tracks of a 1/4 track machine just like in the 1/2 track case. The compromise is a degradation in the S/N ratio of the resultant signal not being as good as one would find with a full track head or a 1/2 track stereo transfer. The Diamond Cut CNF will be able to make up for much of the deficiency in S/N that results from this sort of transfer and the results can be quite adequate and pleasing.

[Craig Maier]

Reel to Reel Half Track Monophonic Magnetic Tape Media

A significant imrovement in tape recording technology was made in the early 1950's with the advent of half track monophonic (monoral) recording. This doubled the amount of time that a single tape could contain. It produced a so called "Side A" and a "Side B" which was really a misnomer. The same side of the tape media (the side having the iron oxide thereon) was used for both so called "sides of the tape", it was simply that that the full track was divided into two sectors, one above the other. Thus, after recording on one "Side" the user could flip the tape and record on the other "Side" which simply used the reversed relative position of the tape with respect to the head(s) gap(s). These tracks were in a so called "stacked" configuration, one being above the other after both sides had been recorded on.

These tapes, when recorded on both "Sides" were not downwardly compatible with full track tape machines in that both tracks would be heard simultaneously, one in forward motion with the other being reversed making for a very confusing and almost indecipherable sound. This format was very popular throughout the 1950's and was even used in the early '60's for Audio-Visual recorders like the famous Wollensak model T-1500 found in almost every school system in the United States.

These tapes can not be transferred with old full track machines without machine modification (replacement of the playback head). Half track mono machines can still be purchased for a very reasonable price on ebay. If you own a professional 1/2 track stereo machine, you can perform the transfer just fine but for the fact that one of the two tracks will sound in reverse. But, the Diamond Cut "Reverse File" feature can be used to correct that problem. Of course, you can also transfer using the 1/2 track machine one track at a time but this will take you twice as long to do the job.

Also, these tapes can be transferred using standard 1/4 track Stereo machines with some degradation in S/N ratio. This loss in S/N ratio (increased "hiss" levels) can be reasonably corrected with the use of the Continious Noise Filter. Most 1/4 track Stereo machines used the "staggered" head configuration. This will result in the ability to transfer both sides of the 1/2 track monophonic tape simulaneously with one track sounding in reverse. However, a few of the earlier model 1/4 track stereo recorders used a "stacked" configuration. This will allow only one track to be transferred at a given time. Thus, two passes of the tape will be required on machines having the "stacked" head configuration in order to capture both sides. But, the advantage of the stacked transfer method is the maintanence of a better S/N ratio when both output channels are summed together in the Diamond Cut Software.

A little hint is in order here which will help save time. When transferring 2 track mono tapes with 1/2 or "stacked" 1/4 track tape decks, both channels are transferable simultaneously. After the transfer, use the Diamond Cut "File Split and Recombine" feature (more information can be found on page 108 of your users manual). This will allow you to create two discrete files after the transfer of both tracks to your hard drive. After splitting the files, then simply use the file reverse feature to place the reverse file back into forward time.

[Audyossey]

An historical footnote (in stereo)

Magnetic tape recording was invented and in use by the Germans during WW2....

Just for the record, the Germans also made stereo recordings on magnetic tape during the war. I can't find it right now, but I have a recording (on both vynyl and CD) of Beethoven's Emperor Concerto made during the war. If you listen very carefully, there's a quiet passage at the end of one of the movements where you can hear flak guns going off. This was in Berlin.

HB

[Craig Maier]

That is pretty darn neat! If and when you find it, can you send me a short snippet of that sector of the recording?

[Dan McDonald]

When I was at Auburn, I supervised a thesis for a guy who traced the development of audio tape. He'd gotten interested in it because John Herbert Orr, the founder of either "Shamrock" or "Irish" tape (I always get those two mixed up) lived in the area. He had commanded a squad of soldiers (I believe an international contingent), whose goal was to capture a German radio station and figure out what they were using to record with. They finally captured one at the end of the war, and brought the equipment home with them.

They used a stockpile of tape for a while, then realized that they didn't know what to do when they ran out -because they didn't know how to make it, so he tracked down the German scientist who had made it, and he wrote some of the formulas down on the back of an envelope. Orr still had that envelope hanging up in his factory some 20 years later.

Orr was known as a little bit disorganized. In an interesting sidenote - When Ampex decided to go into videotape business, they requested tape samples from every manufacturer they could find. Orr sent them a sample which was far superior to anything they received from others, and they used that sample at the famous NAB convention when they demonstrated videotape and got a number of orders directly from that demonstration. After the convention they ordered more of the tape from him, and it turned out he had not kept the formula for it... it took them some months before they could duplicate it. Eventually, Ampex got a little tired of dealing with him, and bought his factory. That's why Ampex's tape facilty is/was(?) located in Opelika, AL (a few miles from Auburn).

Dan

[Craig Maier]

Interesting. Is it also your understanding that the original German tape was paper backed? That is my understanding from discussions with Les Paul on the subject.

[Dan McDonald]

I don't know about the original German tape for certain - but I think that's right. I was supervising that thesis over 20 years ago, so some of the details are a bit foggy. My dad might know this, actually, as he was in communications during WWII. I'll ask him about it. I seem to remember that we had some paper-backed audio tape around the house when I was a kid.

Les Paul probably knows, though. At least I'd take his word for it.

Dan

[Craig Maier]

Monophonic Compact Cassette Tapes

The Compact Cassette tape format was introduced by Philips in 1963 and hit the mass market around 1965. Originally developed as a general purpose spoken voice recording medium, it developed ultimately into a high fidelity technology which competed head-on with the Vinyl LP. Theoretically, Compact Cassettes, when outfitted with the best technology including Dolby noise reduction, could achieve a reasonably flat frequency response of 30 to 16 KHz with 65 dB S/N and 0.1% wow and flutter values.

Early Compact Cassettes were monophonic, with each track consuming 1/2 of its 1/8 inch wide tape. Later, a stereo incarnation was developed consisting of a "stacked" head configuration (stacked represents a 1/2 and 3/4 head gap positioning). This allowed monophonic tapes to be completely compatible for playback on stereophonic machines.

When playing back and transferring monophonic Compact Cassettes, you will not be able to benefit from the time savings of capturing both sides at the same time as you were able to do with some reel to reel tapes (see seperate thread pertaining to that subject). However, effectively, you will enjoy the advantage of transferring almost the entire mono track with the stereo playback machine head resulting in very little loss in S/N ratio.

If you choose to modify your machine and transfer flat directly from the playback head, note that the following de-emphasis EQ's must be applied using the Diamond Cut Paragraphic EQ:

Ferrous Tape: 120 uSec
Chrome and Cobalt Tape: 70 uSec

Some Notes on the Transfer of Monophonic Cassettes:

1. Demagnetize your cassette tape deck heads before playing an old archived cassette tape. Also, clean the heads with isopropyl alcohol and a cotton swab.

2. Transfer it to your computer on its first playing, just in case something bad happens to it during the process. That way, you will at least have something which is obviously better than nothing should the tape break.

3. You can improve your transfer of old cassette material by adjusting the azimuith of the playback head on a tape by tape basis. Adjust this (one of the three screws on the playback head mounting plate) for the best and brightest sounding "highs".

4. The best transfers will not occur by playing early monophonic cassette tapes on original mono equipment. The reason for this is that the original equipment used tape heads with relatively large gaps. Modern cassette decks use much smaller gaps. Therefore, better high end frequency response will be realize by using modern cassette players on very old mono tapes.

5. Never transfer old mono cassettes with the Dolby system turned on during playback. These tapes were not encoded with Dolby and therefore should not be played back in that manner. If you do so, you will loose much of the top end of these recordings. Remember, tape hiss can be reduced later by applying the Diamond Cut Continuous Noise Filter or the EZ Clean Filter after the transfer has been performed.

[Audyossey]

That is pretty darn neat! If and when you find it, can you send me a short snippet of that sector of the recording?

Your wish is my command. With any luck it will be attached to this post as a .zip file.

The recording was made in the Autumn of 1944 in the Haus des Rundfunks (Broadcasting House). The pianist was Walter Gieseking with the Gro?er Berliner Rundfund Orchester conducted by Artur Rother. It's been released on records on several occasions and on CD at least twice including one from the Audio Engineering Society in 1993 when Helmut Kr?ger, its engineer, was made an honorary member of the Society at the age of 88. Interestingly that version (of all versions!) is recorded off-speed. Part of the first movement is at the wrong pitch.

The specially equipped AEG stereo recorder ran at 77 cm/sec (30.31 in/sec) and had a dynamic range of 60 dB. Its frequency response was 50-10,000 Hz with harmonic distortion under 1.5%. Three microphnones were used, left, right, and center, but the center one was used for auditioning only.

The frequency response caught my attention because I've seen spec sheets for American movie theater amplifiers used in this time frame that only run to about 7,000 Hz. Kr?ger remembered making 2- to 300-hundred stereo recordings in the last two years of the war, but only five are known to have survived, this one being the only complete work in that group.

Turn up the volume and you'll hear the antiaircraft guns behind the piano.

HB

[Craig Maier]

Hi - thanks for finding the piece. But, I do not see the file here. Maybe you could send it to me at my email @


dctools@aol.com

Maybe it did not remain attached because it was too big for the bbs system here.

[Craig Maier]

Thanks for sending that. It is really interesting. I am on a business trip and only have my laptop but can still hear the sounds of war in the background! I am looking forward to hearing this on my JBL Studio Monitors and 18 inch JBL subwoofer when I get back home. BTW - I would not be surprised if the mics were Telefunken U-47's, my favorite microphone. If you have ever used a pair of these, you will know what I am talking about. They produce stunning clarity and the sense of presence.

This recording shows an interesting human side of things too. The idea that these folks are interested in recording classical music while their city is getting pounded is quite weird, but maybe understandable as an escape mechanism. It's fascinating, indeed.

ps - this is one instance wherein you DO NOT want to remove the background noises with DCART!

[Audyossey]

Thanks for sending that.

My pleasure. I had fun listening to it on headphones, and couldn't resist taking it downstairs to the "home theater" (of sorts) and playing it deafeningly loud. Hadn't heard it in a long time. I think the last time it was on the radio.

BTW - I would not be surprised if the mics were Telefunken U-47's, my favorite microphone.

Don't know about the mics, but the sound is glorious. For me simple one- two- or three-point miking is the gold standard of orchestral recording.

Apparently RCA Victor did a lot of one-point miking in the days of 78s. Those were the ones which were so often praised as the best in the business. I spent a few months working in the Television Division of the Transportation Training School at Fort Useless (whoops! "Eustis") Virginia. Sergeant Groves was my supervisor. (As far as I know that was his only name. After all I was a Private and he was a Master Sergeant.) He told a story about how that technique came to be adopted or refined at RCA.

At one time his family had a small record company in the hinterlands, and that's how they miked their records. It was the only way they knew to mike, and besides they didn't have the wherewithal to do much else. They got very good at it.

Then they had a hit record. I forget what it was, but I recognized it at the time as a minor hit of the period. Next thing they knew they got a phone call from the engineers at RCA. They loved that sound and felt it had something to do with the success of the record. Could the Groves folks explain how they did it? Well the family didn't much care. They thought the RCA guys were kinda crazy. But the explanations over the phone didn't help the engineers at RCA very much, so RCA paid for them to come out to Camden or whereever and show them what they were doing. So they went out and showed them their method for finding the sweet spot for placing the mics, and RCA used their methods thereafter.

Well, I had to believe him. After all, he was a Sergeant and I was a Private. But it's really not as farfetched as it may seem at first glance if you've ever read anything about how the record business, and small companies in particular, operated in those days.

HB

[Craig Maier]

Quoting HB -

"He told a story about how that technique came to be adopted or refined at RCA."

--------------------------------------------------

I believe that these were called the "You Are There" series of RCA releases. I have at least one of these and they are terrific. Three mics is the way to go in that environment. More mics just seems to create sonic confusion at the mixing board, if you know what I mean.

[Audyossey]

...I believe that these were called the "You Are There" series of RCA releases.... and they are terrific.

Then of course, there are the records that RCA accidentally recorded in stereo. They were made when RCA had its abortive run at LPs in the mid-30s I believe. (For the uninitiated, these were 33 rpm shellac records with the standard 3-mil groove.)

For some reason, the LPs and singles were recorded at the same time, each type from its own mike. In the 70s or early 80s a record collector who had both the 78s and the LPs noticed a slight difference in the sound of the two versions and matched up tracks from the LP with the corresponding 78 versions. The result was a stereo recording.

I heard the story on NPR complete with examples, and the effect was indeed stereo, albeit just barely. The two mics were evidently quite close together. As far as I know, the company has never attempted to reissue any of these accidental stereo pairings in spite of requests to do so.

HB