Order of the Bath

Basic recording on a PC should be a fairly straight forward task. There are plenty of tutorial web pages around which tell you how to connect your equipment, such as a tape player, to the line-in socket (not the microphone socket) with the appropriate lead. Some even remember to remind you that most turntables require a special pre-amp.

There is, however, a big gap in most instructions (the ones I link to above are the better ones). I will use the standard windows tools as an example but your sound card may provide its own version. When setting up the recording you are presented with a “Recording Control” window (one route to find it is Control Panel—Sounds and Audio Devices—Audio—Sound Recording—Volume.) On here you would un-tick the Microphone Select and tick the Line-In Select then, just above it is a Volume control. What do you think it does?

There are supposed to be standards for audio interconnection but they have not been consistently adhered to by manufacturers. In the golden years of Hi-Fi (mid 1970’s) there was a de-facto line-level sensitivity of about 200mV and you could buy virtually any combination of equipment and it would connect together. This was the boom of mix-and-match. Prior to that it was a bit more hit-and-miss but the critical change was when the CD player was invented. Whether it was to hype the supposed quality of CD or some other reason I don’t know but they consistently had a much higher output. People connected them to the AUX sockets on their amplifiers and were blown across the room; isn’t it loud and clear! But after that, they had to remember to turn the volume down when switching over to CD; I am still doing it. This didn’t matter a great deal because the analogue circuits are flexible enough to cope though the more discerning can tell that they are really being over-driven causing a brittleness to the sound.

Getting back to the PC, sound cards do seem to adhere to the standard which, by the way, is -10dBV sensitivity for domestic audio. Instinct would suggest that the volume control is like the record level on a tape recorder or the gain control on a mixing desk. That is mistaken; those controls are passive attenuators BEFORE the active pre-amp circuitry. The control you see here is a digital control AFTER the Analogue to Digital Converter (ADC). The important point is that if your input signal level is too high then the damage has already been done. The overload will have been converted into very nasty digital distortion. In fact the volume slider is practically useless as the standard one is not even calibrated with a zero mark. I presume that above a certain point it offers gain to boost signals that are a bit quiet but, unless you are mixing it with other input signals in real time (in which case you really need a lot more sophisticated equipment) then setting it below the imaginary zero mark is unnecessary—why would you want to waste any of the signal you have been given.

My problem is with an old reel-to-reel tape deck (remember them?) which is an early 1970’s model with a very high output. I realised when I bought a decent sound card that had calibrated controls (E-MU 0404), that I was well into the red before starting. So what to do about it.

You could follow some advice given and use the headphone out socket but some, like mine, do not have a level control, and even then you are subjecting the signal to an often low quality headphone amplifier. You could try sending the line signal via an intermediate pre-amp but this may pass the signal straight through unless you have an adjustable line level output; mine doesn’t, and in any case it would be a bit of a nuisance to extract it from the Hi-Fi system. A third possibility is to use a mixing desk. These are designed to handle a wide range of input levels but not many people have one in the cupboard (and I discovered that mine was broken).

The ideal solution would be a passive attenuator between the deck and the line-in socket. I have found one cottage industry maker of these which he calls Goldenjacks. He does them primarily for the audiophile improvement of CD reproduction but he reports that he is selling more and more for our purpose. Mine haven’t arrived yet but I have ordered a pair of -10dB “source end” plugs and I fully expect them to do the trick. I thought initially that I would need a variable control but really it is a case of you either need attenuation or you don’t; in which case they can be removed. If you need more than 10dB (1/3 the signal level) then you have a more serious problem.

This entry was posted on 21 Sep 2007 at 09:56 by Rick and is filed under Hi-Fi & Music. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.