Home Recording With Digital (Part 2)
Overdubbing With The Sony PCM F1
Article from Home & Studio Recording, January 1984
Connecting up the machine and general operation needs some thought. As mentioned earlier, the PCM F1 meters the playback VTR feed only. Also, your mixer will need peak reading meters to monitor the combined output signals, because VU meters are inherently sluggish, and are not designed to read very fast transients, if however, your VU meters are augmented by a peak LED of known triggering level (ie +6dB) these will suffice.
There is a further complication however. The F1 meter will show the pre-emphasis that has been applied to the audio signal prior to D/A processing. There is around 7dB signal boost at 10kHz compared to the level at 1kHz which means that, should you have not allowed for this when setting the nominal record level at which you are working, you will hit the digital 'crunch point' very easily if there is any noticeable HF (high-frequency) content in your music.
My experience shows that it is best to take your 'zero level' on the mixer as -20dB reading on the F1. Working with peaks around 8dB above this (-12dB) is then sensible as the F1 dynamic range will be fully used due to the metering pre-emphasis. You have in excess of 90dB to play with, remember!
In the setting of levels the requirements are as follows; how you implement them will depend upon your particular mixer. You'll need a source of tone, ie. an oscillator giving 1 kHz at a suitable level. Initially, before any recording takes place, couple in the oscillator to the channel to be used for the F1 playback and set everything up so that the mixer's meters read zero VU (or whatever operating level you have chosen) and the PCM F1 reads -20dB. Record the 1kHz tone for several minutes.
Then replace the oscillator connection with the playback VTR - your mixer should still read 0VU when the recording is actually replayed. If not, readjust your gain levels and for confirmation copy the tone onto the record VTR. Play this back and check that the level around the loop is still constant.
This operation highlights the beauty of digital recording: there are no levels to be set between the playback VTR and the F1, nor are there problems with azimuth head adjustment. The test tone you've recorded will be as 'pure' on playback as the original, with no modulation noise or side effects that we've come to accept from analogue.
The accurate setting of record levels 'around the loop' ensures that there is no unnecessary reduction in level around the system, or worse still an increase, as this could quite easily lead to overload and system 'break up'.
When recording is underway and you are playing back your first layer, the new inputs can be controlled and the whole viewed on the mixer meters at the same time as being audibly monitored on speakers or headphones.
It could be that as you add more overdubbed layers the signal level begins to approach the overload point. The solution is to simply drop the level of the mixer output a few decibels, as this won't make too much of an audible difference as far as noise enhancement goes.
Another possible tip is actually to record each transfer one dB or so below the original level to compensate for level increases from the overdubbed layer. In theory, two identical instruments in sync and in-phase would produce a 3dB level increase when combined onto a recording. In practice, this is unlikely to occur so the average increase is slightly less than this.
It would seem to me that with the Sony PCM F1, or the alternative PCM 701, and a couple of Beta format video recorders, the capital outlay is certainly justified, considering the class of performance obtained - certainly compared to an eight track with stereo mixdown on reel to reel. Bear in mind that you may well be able to borrow the family VTR and that of your next door neighbour!
VHS machines can be used but some suffer from a curious 'run back' feature which you would have to allow for in any cueing. Mixed Beta and VHS machines will obviously mean alternate record and playback use, needing the connections to be re-jigged each time. To overcome this you can quite easily make up a switching system, as I have incorporated in the portable overdubbing suite I use for mastering Whitetower records.
Feature by Mike Skeet
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