Well, that's not quite true, Pandora's box was the source of all the problems, this one just points them out for you.

The Tapetalk box is by no means a newcomer to the recording world, but the model reviewed here is a new addition to their range and is aimed at the smaller professional studio and serious home user. If you still don't know what I'm talking about, it's all to do with metering. Once upon a time...

In a typical studio you will find dozens of meters, either VU or PPM, but they all tell you just one thing - what's happening to the dynamic level. More sophisticated desks might have an inbuilt phase meter but they aren't all that common. Whereas most meters tell you something about absolute level, the Box tells you things about phase and relative level (in other words - balance). But firstly, why do we want to know about phase at all?

The Phase

Despite the increasing popularity of CD, plastic records are going to be with us for some time to come and in the cutting of a disc, the phase of the left and right channel signals is very important. The reason for this is that a single stylus tracks both left and right channels by responding to directional information in two planes at right angles to each other. This movement is then translated via a couple of pick-up coils, also set at right angles, into two separate electrical signals. One restriction of this system is that the phase between the left and right channels must not be greater than 90 degrees, otherwise the stylus movement will be resolved into a vertical component which tends to bounce the stylus out of the groove: clearly an undesirable state of affairs. This is particularly true at low frequencies where the stylus excursion is greater.

In a stereo recording, there's bound to be some phase or amplitude difference between the channels, otherwise they would both be carrying the same signal (known in the trade as mono). The bigger the phase differences, the more pronounced the stereo effect, and this goes for both true stereo and electronically simulated stereo. The trick is to know how much you can get away with. For example, by actually inverting the phase of a signal in one channel to give 180 degrees of phase shift, an apparent stereo spread can be created which actually seems to be wider than the speaker positions, but would give us severe cutting problems. However, for CD or tape releases only, there is no reason at all not to indulge in such tricks. But enough of the hors d'oeuvres, let's get on to the main course.

The Box

The object in question appears as a nicely finished wooden box, a little smaller than an Auratone speaker. Powered by a mains adaptor type of supply via a DIN connector, there are two sets of phono inputs on the rear panel so it can accept high or low level signals (line or speaker outlet), and the front panel consists of a matrix of coloured LEDs. There are no controls to set up; the skill lies in translating the display.

There are 100 separate LEDs in the display, 43 green, 15 yellow, 17 amber and 25 red. What can it all mean?

Well, it's partly to do with lissajous figures with which you will be familiar if you have ever used an oscilloscope, but which you may never have heard of otherwise. Basically, a sine wave fed into both the X and Y (horizontal and vertical) axes of a scope will produce a straight line display if both are in phase. If the relative phase changes, the line opens up into an elipse and eventually into a circle. If the phase is continuously changing, the picture looks like a side shot of a hoop rotating in space. You've probably seen them on Dr Who being used to repell the Scrotons... A scope is used in this way to set up head azimuth using a test tape. By monitoring the two outside tracks on the tape with a test tone playing, the head azimuth can be adjusted until the scope proclaims that the replay signals are in phase. Of course you start out with a low frequency and work up, otherwise you could end up with the head on a tilt but still have zero phase error because you're a complete cycle out. Okay, so where does the Box come in? Well for a start, you can use it instead of a scope to set up your heads. Feed the same signal into both inputs and the centre line of red LEDs only will light. Absolute level isn't too important because the Box starts to auto-range if the signal gets up past the yellow LEDs. All you need is enough signal to give a healthy display. If the inputs are then fed with the same signal but one is phase shifted, the line starts to open out. The result isn't quite as artistic as on a scope and at 90 degrees shift you end up with a square rather than a circle but the principle is the same. If you're setting up your heads, you just make the necessary adjustments whilst watching the display and get the display back to a straight, vertical line. The manual shows you which patterns to expect for what amount of phase shift and it's dead easy. If the phase exceeds 90 degrees, then the display ceases to join up at the top and the gap gets bigger, the more the phase is increased. At 180 degrees, the display shows as a letter V with only the outside rows of LEDs lighting.

Now consider a single signal fed into one side but not the other.. We just get a straight line along one of the outside rows of LEDs like half a letter V. This is great for checking the balance between two supposedly identical signals such as the outputs from a two channel processor or an amp with suspect attenuators. If the signals are exactly in balance, we get our vertical straight line but if they're not, the line leans to one side or the other depending on which side carries the largest signal. Doing this test, you'd be surprised at what imbalances there are in your system and how they add up. Also, if one signal path has less headroom than the other and is running into clipping, the display will lean away from the side that is clipping. Modest signals will generate the straight line display but this will kink at the point where the clipping starts to occur. The same test is valuable for checking that stereo limiters are limiting at the same level.

Dynamic Metering

So far we've looked at the Box as a diagnostic tool for checking out your system or for aligning gear but it's also very useful as a dynamic programme meter. When a composite mono signal is fed into both inputs, amplitude changes are registered by the central vertical line which will bob up and down a bit like a traditional PPM meter (the LEDs represent 3dB steps until the autoranging comes in above the 6th LED). However, a stereo music signal will cause the line to spread into a flame-like shape which will flicker as the programme dynamics affect the display. By checking that the average flame position is somewhere near centre, you can confirm that your balance isn't going to be lop-sided. The wider the flame pattern, the wider your stereo spread. But a word of advice here, turn off your stereo digital reverb first as this makes everything look wide. Use the Box to position separate bits of the mix at a time, then check the overall balance and finally add reverb. If you've done anything that is going to cause cutting problems such as applying deep stereo flanging to the entire rhythm section, then you will notice that the flame changes. In this event, you have the choice of moderating the flanging depth or panning the two sides towards the centre until the problem goes away. Indeed, by inverting the phase of one of the inputs to the Box, you get a display that actually simulates the movement of the record cutting stylus. And by no means least important, the light display will impress your clients.

Conclusions

The box can reveal quite a lot of things about your system that conventional metering cannot, and even if you don't get heavily involved in specialist applications, it's still worthwhile if just to check stereo spread, balance and phasing. However, it really can do much more than that and it may well be worth plumbing one into your patchbay rather than simply leaving it connected to the desk's left/right outputs or to some point in the monitoring system. This way you can check the outputs of your stereo processors as you set them up. The more you think about it, the more applications you can think of, and the fact that you can also use the Box to align your tape machines very accurately without the need for a scope is a big point in its favour. Even if you can afford a scope, you may well find the controls confusing, whereas the Box has none to worry about! You can even use the Box in conjunction with a flat response mic to equalise your room by feeding the mic output via a suitable pre-amp into one channel of the Box and the output of your monitor amp into the other. By using an oscillator to generate the frequencies of the bands in your graphic, you can set up one band at a time by balancing the electrical and audio signals. It's a bit slow and you may have to go through it two or three times due to inter-band interaction in your equaliser, but it can be done.

This is an ingenious British product that can be used on a variety of levels though it takes a little while to get to know it well enough to get the most out of it. Its only real disadvantage is that it takes experience to be able to evaluate the display correctly. I left one connected to my stereo for a week and it was interesting to see how different records were represented. You could use the Box to check through your whole system, but in any event, it is still worth having one just to save the embarrassment of delivering a mono tape to a client, and all because you'd forgotten to press a couple of buttons on the desk.

The Box (including adaptor) costs £203.53 including VAT.

Further details are available from: Tapetalk, (Contact Details).