Kramer Master Tape White Paper

Introduction

When Waves started a hardware modeling project with Eddie Kramer, it was always their intention to create a model of the original recording chain from Olympic Studios in London that Eddie used on his great recordings of Led Zeppelin, The Rolling Stones and Jimi Hendrix. The model of the Helios Console Channel was challenging, resulting in the Waves Kramer HLS Channel. Next was the modeling of the famous PYE compressor which was released as Waves Kramer PIE Compressor.

Missing from this ‘golden’ chain was the classic American tube analogue tape machine used for these recordings. Waves acquired what they believed was the right machine and set about modeling, knowing it would be difficult based on what was already on the market. As it turned out, the task was much more daunting than anticipated and Waves’ first attempt, the initial Kramer Master Tape, was withdrawn shortly after being introduced into testing. It turned out that this third piece of the Kramer Olympic chain was going to be the hardest.

Waves discovered (along with the guidance of some of their Beta team) that they were missing a number of things, each one extremely complicated by itself, and in total representing a huge challenge. Thanks to the guidance of Bob Olhsson and John Haeny, Waves were ultimately directed to the correct transport and tube electronics. With Bob’s help, one of these rare beasts was found in Florida owned by Eric Shilling. Eric kindly agreed to let Waves do some preliminary testing to ensure that this machine was producing the sound that both Bob and John had missed in Waves’ first effort.

To clarify what appears to be a contradiction regarding the Olympic tape machine being an American product in a British studio, it should be made clear that at the time Eddie Kramer was working at Olympic Studios in London, it was these American tape machines that Olympic and their clients were using as master recorders.

This world famous tube tape machine was the mainstay of the recording industry (particularly in America) and was used for literally thousands of hit albums and singles over more than two decades of recording. For example in 1954, an early tube analogue reel-to-reel tape machine recorded the historic first single of an unknown truck driver named Elvis Presley, "That's All Right" at Sun Studios in Memphis. This same reelto-reel tape machine was also the backbone of the earliest days of multi-track recording. The first of the 8-track versions of this recorder was custom built for and sold to Les Paul for $10,000 in 1957, and was installed in his home recording studio. It became known as the "Octopus”. 8-track serial number #3 of the same machine was sold to Atlantic Records at Tom Dowd’s insistence in early 1958. Atlantic Records was the first record company to use a multi-track recorder in their studio on a regular basis. Just pause for a moment and contemplate all the great recordings that came out of that Atlantic Records recording studio. If they ever were to induct a tape recorder into the Rock and Roll Hall of Fame, this would be the machine!

With the modeling project still appearing workable, it turned out that the recording curve, tape speed, tape emulsion, tape thickness, flux or level recorded on the tape (more later), and the bias settings all greatly impacted the final result. So again, with Bob and John’s help, endless discussions and tests were made regarding tape types and alignment techniques until what Waves were going to model was finally settled. Over time and with much experimentation, they made sample recordings that both Bob and John agreed had established a solid baseline from which to proceed. It would be these initial samples of the test recordings that would be used for detailed comparison to ensure that each model was performing accurately.

Once again, Eric Shilling came to the rescue and agreed to do the massive testing and modeling runs required to model the two primary tape speeds, a number of tape emulsions plus variations in flux and bias settings as well as approaches to alignment techniques.

With the modeling files in hand, Waves began the excessively complex task of creating models, not only of the variety of analogue tape recordings, but the variety of bias, flux levels (tape saturation) and speed settings. When Waves began evolving early stage Alpha plugs, they required painstaking subjective analysis by comparison to the original samples recorded on the original tape machine and then through feedback to the development and engineering team, the models were honed. Because Waves felt they could best do their development using only one platform at a time, they chose to do their final development on the Macintosh, at which time Bob, who primarily uses a PC, offered to take a back seat. John volunteered to take up the slack and became a more or less full-time co-developer of the Kramer Master Tape plugin.

What Was Modeled And How Does That Affect The GUI And The Operation Of The Kramer Master Tape?

Tape Type

Waves modeled 3M Scotch 207 tape as it was considered an excellent match for this machine. Originally 3M Scotch 111 tape would have been the tape of choice for many during the early days of analogue tape recording. There were other earlier tape types that were exceedingly popular as well - for example, 3M Scotch 201/202/203 was used extensively by Motown, but sadly it was no longer available in a sufficient and durable enough quantity for this project. Waves was also able to source an amount of an earlier tape stock, 3M Scotch 131, but sadly the quality was poor and it did not hold up during the modeling process. Because the members of the Waves team had extensive experience with 3M Scotch 206 (a 1.5 millimeter base) and 3M Scotch 207 (a 1.0 millimeter base), 207 was selected because of the slightly thinner base, although perhaps subject to greater print-through (clearly not an issue for a tape modeled plugin), 207 provided a more intimate recording and playback head contact (called ‘tape wrap’) and thus produced a more extended high frequency response. Fortunately John Haeny had a sufficient supply of virgin 3M Scotch 207 stock for the purpose so off the shipment flew from Australia to Florida.

Tape Speed

The original machine’s transport has 2 speeds: 15 ips (inches per second), and 7.5 ips. 15 ips was the default professional standard providing the best high frequency response and the lowest noise. 15 ips has a gentle roll off at around 16 kHz. 7.5 ips was the minimum reasonable professional quality speed for studios and there was also a fair amount of equipment for the home that operated at 7.5 ips. 7.5 ips has quite a high frequency loss with a roll-off starting at around 8 kHz, but 7.5 ips managed to preserve low frequencies better than 15 ips with a slightly more ‘solid’ bottom end and therefore was widely used in rock recordings in the 60’s and 70’s.

When switching between the 2 speeds you should expect to get a very much improved high frequency response with 15 ips when compared to 7.5 ips but perhaps a somewhat less tight low end. Note that 15 ips will also provide less THD (Total Harmonic Distortion) than 7.5 ips. There is also a shift in the frequency of the noise by an octave between 7.5 ips and 15 ips, with the noise at 15 ips sounding an octave higher than 7.5 ips. The significance of this difference has always been argued, with some preferring the noise signature of 7.5 ips and others preferring the noise signature of 15 ips. As time progressed and 30 ips became popular, many used 30 ips because as the noise shifted upwards yet another octave from 15 ips, it moved further away from the fundamental musical frequencies and thus became less obtrusive. Experiment and form your own opinions on the issue of speed vs. noise vs. frequency response.

Pre-Emphasis Curves

At the time of the modeled tape machine’s popularity, there were a number of magnetic tape recording standards in use worldwide. Because of the inherent limitations in analogue tape recording, these curves generally applied high frequency pre-emphasis equalization during recording and then applied a high frequency post-emphasis during playback. The net result of this was to maintain high frequency response according to the standard being used with the added benefit of also reducing tape noise. The most popular standard in Europe at this time was CCIR; in America, the standard was NAB (National Association of Broadcasters). The machine at Olympic, as best we can determine, was a NAB machine although the manufacturer would provide CCIR machines on special order. Additionally, NAB was the standard used for the vast majority of the American pop recordings done on this machine. Because the NAB standard provides the most accurate sonic signature of this legendary American tape machine, the NAB standard was chosen by Waves for the Kramer Master Tape model.

Bias

Defined: Bias is a high frequency signal, typically between 40 kHz and 150 kHz, applied to the record head along with the audio signal when an audio track is placed into record. The bias current solves a critical problem when recording to analog tape. When the amplitude of an audio signal passes through the zero voltage crossing, the magnetic field created by the record head is not strong enough to polarize the magnetic oxide particles on the tape. Thus, a distortion of the original audio signal is introduced. To minimize this distortion, the bias current is applied to break down this resistance to polarization. The audio signal can then be recorded more accurately without the effects of low level distortion. The amount of bias current applied is critical to the frequency response and distortion characteristics of an analog recording.

Waves modeled and have provided you with two bias settings. “Nominal Bias,” the manufacturer’s recommendation for bias adjustment (directly from the original operator’s manual for the modeled machine) was recommended in the early years to try and reach the best recording levels with the minimum amount of distortion and the maximum frequency response. This setting produced a fairly low noise level (around 60 dB lower than the peak signal), and around 2 to 3 dB of high frequency loss with a moderate amount of high frequency distortion.

During the ’60s, after a number of years of working with these tapes, many professional studio engineers and technicians discovered that by overbiasing (increasing the amplitude of bias signal) by only a small amount, they could improve the high frequency response and at the same time lower the noise level. This was called “Over Bias” and each tape type, studio, recording engineer and technician had their own way of calibrating the bias to achieve their preferred sonic qualities.

For the Kramer Master Tape, we modeled the -3 dB over bias, which was agreed by most engineers to be the point where you got the best high frequency response, least amount of distortion and best signal to noise ratio on 3M Scotch 207 tape. (Actually -.7 dB at 700 Hz for 15 ips, but set at -3 dB at 15 kHz for accuracy. You adjusted nominal bias to accomplish the peak level of the signal and then continued beyond the peak until the level began dropping by the desired amount, therefore the term ‘over bias’. The bias adjustment for 7.5 was done one octave lower at 350 Hz or 7,500 Hz and at -20 dB to avoid excessive high frequency saturation.) When you switch from “Nominal Bias” to “Over Bias” mode, you should expect to hear a bit less noise, clearer high frequencies (reduced distortion), and a bit more overall dynamic range (and clarity, once again the result of less overall THD).

Flux

Defined: The magnetic flux density recorded on a tape (level). The standard unit in measuring the amount of magnetic energy recorded to tape is expressed in NanoWebers per meter (commonly abbreviated as nWb/m). When picking an operating level for tape (flux/level), the general rule is that the higher the operating level, the further away you are from the noise floor but the closer you are to the point of distortion. This dynamic is highly dependant on the tape stock being used. For a detailed dissertation on magnetic recording flux and flux-frequency measurements please use this URL http://home.comcast.net/~mrltapes/mcknight_flux-and-flux-frequency-response-measurements.pdf

Flux is the magnetic density recorded on the tape per meter (nWb/m), the higher the flux level - the higher the recording level on the tape. In order to reach higher recording levels you need to have tapes that can manage a higher flux level (many modern tapes can reach very high recording levels with minimum distortion with the added benefit of reduced noise or ‘tape hiss’).

The manufacturer initially established a recording level for recordings made on their machines during the 1950s. This was called Standard Operating Level. This recording level was at a flux level of 185 nWb/m. All early alignment tapes were Standard Operating Level or 185 nWb/m signals and eventually became the standard for all magnetic tape recording. As tapes were developed to handle greater and greater flux (or higher recording) levels, the industry continued to rate tape flux levels based on the original Standard Operating Level. For example, a tape that was designed to record signals at 250 nWb/m was said to be recording at +3 dB (over the Standard Operating Level of 185 nWb/m). As a point of reference, since the Flux Control on Kramer Master Tape is calibrated in nWb/m, here is a quick reference guide for comparison (Source Quantegy):

Science aside, early on many engineers discovered that by pushing or abusing the recording levels on tapes, it created some very musical and frequently desirable side-effects, especially in Rock and Roll recording. Tape has a very unique way of going into saturation or overload, whereas digital is basically ‘go or no-go’ with over-modulation producing clipping. As the levels are raised on analogue tape, a number of things increase simultaneously and fairly gradually: Total Harmonic Distortion (THD), Inter-modulation Distortion (IM), Modulation Noise and a mix of other aberrations and for ms of distortion, many of which are still not fully understood. Also, when tape is pushed hard enough, it has a tendency to ‘saturate’ which is a form of compression, unique to analogue tape. Many engineers, even when digital was available, still preferred to record certain instruments on analogue tape (especially Rock and Roll drums) pushing the levels on the tape well beyond their ideal operating conditions to gain this saturation or compression.

Modeling this behavior of changing sonic behavior across a wide range of flux levels was perhaps one of Waves’ biggest challenges. Ultimately they were able to create a continuous flux control that ranges from -2 dB below the Standard Operating Level well into unknown territories, invaluable for a wide variety of special effects.

Since 3M Scotch 207 was rated at between 185 nWb/m or 250 nWb/m (while opinions vary about the ‘ideal’ level for Scotch 207, Waves chose the more conservative level of 185 nWb/m for the Kramer Master Tape default, although they modeled a wide range of flux levels to be able to accurately create the variable flux control), you will find that the plugin will be especially sensitive to settings above the recommended level of the tape sampled. When reaching higher flux levels you will notice that the low frequencies and very high frequencies become more and more distorted as the noise level goes down. Additionally there is another layer of distortion since these increased operating levels also stress the tube input and output stages, giving you the bonus of an additional level of overall “tube distortion.”

Kramer Master Tape is the first tape modeling plugin that has actually managed to create a continuously variable flux control, letting the user sonically understand the changes between different recording levels. Add to this that this is also being done on a fully tube electronics tape machine and you truly have a one of a kind plugin - unique in the industry.

As an added feature, using Kramer Master Tape in the input only mode allows you to add the sound of the input and output tube electronics, minus the sound of analogue tape recording. Increasing the record level as you reduce the playback level (to maintain unity gain) increases the tube saturation of the input and output amplifiers, independent of the flux control (which only affects tape saturation). These controls can be used either in conjunction with the sound of the tape saturation, or without the tape saturation to create just the sound of these unique tube amplifiers operating across their entire range of saturation.

Because of the independence of the flux control and the record level and playback level controls, you have full control over both the tape saturation and the tube saturation while maintaining the level of the Kramer Master Tape track in your mix (using the ‘Link’ function for the record and playback controls).

To simplify the Kramer Master Tape Flux control, just think of it as a ‘tape drive’ or ‘saturation control’. As you increase the flux level on the tape the output of the Kramer Master Tape plugin stays constant at unity gain unless you choose to adjust the output gain control.

Noise

Although the Noise control on the Kramer Master Tape is defaulted to off, it is strongly suggested that you take a listen to it. If this can be said, you may find it to be some of the sweetest noise you will ever hear since it is a combination of the tape hiss generated by analogue tape recording, overlaid by the thermal tube noise of this historic machine’s input and output electronics.

Wow

Defined: Wow and flutter in analogue tape recordings results from the turning speed inaccuracies (FM), and flutter effect (AM) caused from changes in the physical alignment of the tape on the actual recording head, coupled with the ‘slip and slide’ of the tape going through the transport mechanism and a variety of mechanical ‘frictions.’

In a perfect world, there would not have been wow and flutter. Many ‘in the day’ considered wow and flutter the same as surface noise on a vinyl disc - just something negative one had to live with since that was the ‘state of the art.’ But like noise, there are many that will feel that any model is not complete without all the flaws as well. For that reason, Waves has provided you a manual wow control on the plugin’s graphic interface. It is defaulted to the wow and flutter modeled on the sample machine. You can increase it for a somewhat more enhanced effect (although it would have never been too obvious [unless your machine was broken] as it was always a subtlety of the analogue tape process), or if you choose, you can move to a more idealized world and turn the wow off. Having or not having wow and flutter and/or noise has nothing to do with the primary advantages of the analogue tape recording sonics, so use them or not at your own discretion. You will always have the advantages of the Kramer Master Tape sound with or without them.

Something Extra

To sweeten the Kramer Master Tape package, Waves also added a variable delay control (0 ms-500 ms) that routes the tape playback of the plugin back to the input of the Kramer Master Tape. This creates a very basic feedback tape delay effect across the entire signal (the direct signal is always included in the mix). A low pass (LP) filter was added to the delayed feedback path to allow you to filter out any unwanted high frequencies. This delay/feedback feature is intended to be very basic. It does not offer a wide control section, but is believed to contribute additional value to the Kramer Master Tape plugin. Used carefully, this function has the capacity to create some very lovely tape delay sounds. It also needs to be pointed out that the delay is only affected by the Delay Time control in the delay section. It is NOT affected by the running speed of the transport. If you need to ask why Waves included this bonus function, the answer is quite simple...because they could, and they were confident that you would enjoy it!

What To Expect From The Kramer Master Tape

Default Set-Up

The default set-up of the Kramer Master Tape, without any adjustments, will provide identical results to having made your recording on 3M Scotch 207 at 15 ips using a NAB standard curve with an over-bias of -3 dB at 15 kHz and at a recording flux level of 185 nWb/m. This will yield the sound of the basic industry set-up for this machine at the height of its era. The only item remaining for you to decide will be whether or not to have tape and tube amplifier noise, and if so, exactly to what degree.

Of course you also have other options with regard to bias, wow, speed and most dramatically, a continuously variable flux control starting at the ultra conservative setting of -2 dB below the classic Standard Operating Level all the way to some rather massive, heretofore unattainable in a plugin, extreme analogue tape saturation effects.

Meter Transfer Switch

On the face of the meter, you will find a switch that lets you choose whether the meter displays the plugin’s input or its output. This is purely a meter transfer switch and has no effect on the monitored sound.

Mode Switch or Input/Reproduce

In place of the classic record light you will find an illuminated yellow or amber lamp. The label above it will be in the default mode of Repro, which means the output of the Kramer Master Tape is after the model of recording on tape. (i.e., in Repro mode, you are hearing the sound of the playback head reproducing the signal previously recorded by the record head.) In the Input mode, you will only be hearing the sound of the tube input and output electronic stages (or directly through the machine without any tape running). This is not a pure bypass and this sound is, in and of itself, valuable for many applications. Other than the audio monitor transfer and the light being on for Reproduce and off for Input, when in Reproduce the transport reels will also be turning to insure you that you are hearing the result of recording on analogue tape. Should you choose not to have the reels turning, simply clicking on them will turn their motion off.

What Should You Expect to Hear

The sound of analogue magnetic tape recording may be new or un-familiar to some born in the digital age. The goal of the design of all analogue tape recorders was the same - to provide a transparent, colorless method of media storage. The machine we modeled was quite successful in its day, at accomplishing this goal. But because of the state of the art at the time of this machine’s development, it still had a wide variety of limitations: Tape saturation, tape noise, harmonic distortion, modulation noise, phase shift and limitations in frequency response to name but a few.

Although many think that analogue tape will improve the sonic quality of their signal, by today’s standards and measurements it does quite the opposite. Measured by modern technology it lowers the overall resolution of a signal. In fact the signal to noise ratio of an analogue tape recording is not good by today’s standards. It fails to accurately reproduce both high and low frequencies. Its THD (Total Harmonic Distortion) measurements are not good by current standards (more than 1% THD) and yet listeners still find its sound pleasing.

So just why is this sound so desirable? Well for a number of reasons, but firstly, contrary to measurements and the theoretical loss of high frequency response, because of the non-linearity of the NAB standard, coupled with the third harmonic distortion created by the analogue recording process, the ultimate subjective result is a slight increase in the quantity and clarity of the higher frequencies.

Even as digital recording has come of age, and with hindsight 20/20, what many considered to be a limitation of analogue tape recording, has in fact become desirable. Digital has been criticized by many as being clinical and cold sounding, while analogue technology has been touted as sounding warm, clear and musical. Therein lies the big difference in what you should hear in the plugin. Granted, if you want to play with the settings (and please feel free to do so) you can create some very dramatic tape effects of saturation, noise, etc. But by using the Kramer Master Tape with its default setting, it will provide you with an extremely accurate model of, not only tube analogue tape recording, but of analogue tape recording on what many considered to be the premier tube analogue tape recorder of its era.

A description of the sound of the Kramer Master Tape is that it is best ‘felt’ as a warm, sweet and clear musical sound. Start there as your basis and then experiment with the controls to discover all the additional sonic qualities available to you, and choose those that best suit your tastes and your style of music.

In Practical Application

It is not possible to create a model with this level of detail and flexibility and at the same time keep its resource demands low. Running Kramer Master Tape does require a fair amount of system resources as you might expect. If you want to use the plugin on individual tracks, please do so, as there are no ‘rules’ in our art form. But Kramer Master Tape may perform best on sub-mixes of drums and percussion, strings, guitars, vocals and anything that requires analogue ‘warmth and clarity.’ Also, don’t forget what the plugin could contribute to digitally sampled instruments and digital synthesizers. Many will find that across an entire mix and especially in mastering, Kramer Master Tape may prove to be invaluable. The Kramer Master Tape plugin is the result of almost two years of failures and triumphs, and contains the heart and soul of many contributors. Waves’ sincerest hope is that you will enjoy Kramer Master Tape, and that it will become an invaluable component in your sonic toolkit.

Kramer Master Tape used in conjunction with the Kramer HLS and the Kramer PIE finally completes the magic of the original Kramer Olympic Studio recording chain.

Visit http://johnhaeny.com

Written by John Haeny
Based on an original outline by Mike Fradis, Waves Product Manger
Edited by Michael Costa
Bias Definition by Michael White