Crash Course in Analog Tape Machines
What if you were enlisted to assist on an analog recording session? One of my students is headed out of state to do just that. It’s been a year since we’d ‘analog’d’ together, so I figured he needed a few mental refreshing bullets, so here goes…
- Make friends with staff
- LEARN HOW TO THREAD THE MACHINE ASAP
- STAFF will likely do the alignments, but you will want be sure to query the engineer as to the preferred Operating Level, Tape Speed and EQ (details below).
- Take every opportunity to observe when geeks are melding with machine.
- ALWAYS put the machine in SAFE MODE after a take until you are sure it is time to record again.
DAILY MACHINE MAINTENANCE
Heads should be cleaned throughout the session especially at the beginning, so you get a feel for the tape’s condition – even new outta-da-box tape may shed – some more than others – this kills High Frequency (HF) response. Use 99% alcohol or denatured alcohol. Dedicated cleaner may be extremely potent / caustic, so keep far away from plastics (like VU meters).
LOOK closely and you’ll see a technique I use to make oxide buildup – and head wear – visible. I lay a sheet of white paper on the deck plate in front of the headstack. Good, non-glare, overhead light reflects on the paper to the head.
Do not use alcohol on the pinch roller – either a dedicated rubber cleaner or diluted windex / formula 409 on a cloth / paper towel is better. Be wary of pinch roller degradation warning signs – when the ‘puck’ transitions from firm to soft / tacky / gummy.
Be super aware of hidden magnets and their proximity to tape and machine – Laptops, speakers / monitors / tools…
- Tape obviously has no time stamp so keep really accurate notes.
- Set 00:00 at the head (beginning) of the tape. ,
- tapes are stored PLAYED = Tail Out
- Label the reel, label the box, and if you’re handwriting sucks, use your laptop for session logs and make sure to get access to the local printer.
- Tape machines have Erase, Record (sync) and Playback (repro) heads. -’Print’ tones at the head – one minute (minimum) each: 1kHz, 10kHz, 15kHz, 100Hz, 50Hz.
- Insert Leader tape after the tones.
- Waver of more than 1dB @ 15kHz is not an encouraging sign.
- In SYNC mode, The machine will automatically switch to input when recording just like PT!
- Obviously the remote let’s you choose monitor modes – INPUT, SYNC (for overdubs) and REPRO for mixing.
I pretty much use 15 inches per second because it is both economical (a 10-inch reel lasts 1/2 hour) and good for rock because the low frequency response is extended compared to 30 IPS, a speed that does not allow you to push low end, especially kick drum. At either speed, I do not recommend EQ-ing (boosting) low end to tape – esp @ 30IPS – low end boost is better to do on playback.
The first image in this link shows how tape speed affects frequency response.
Standard operating levels are expressed two ways: in nanoWebers per meter (185nWb/m, 250nWb/m, 320nWb/m or 520nWb/m) or in the amount of dB above standard operating level, as ‘plus 3, plus 6 or plus 9.’ For example 250nWb/m is +3 above 185nWb/m. Follow this link for details…
If, for example the test tape is @ 250nWb/m, but the eng wants to run 3dB higher (approx 320nWb/m), set the test tape ref tones for REPRO and SYNCH at -3dB VU.
- BEFORE record alignment, a known +4dBu reference tone is sent to all channels.
- Machine is switched to input and INPUT CAL is adjusted for 0VU.
- DURING Record alignment, machine is switched to REPRO. Adjust REC CAL / Level for 0VU.
- Record alignment begins with bias – read article above as this should be done by staff – then INPUT cal, record level and finally by HF record level..
- BIAS is primarily to minimize low frequency distortion and maximize punch. BUT, Bias affect High frequency response as well.
- Bias is typically adjusted for a peak @ 10kHz and then increased (CW) until 10kHz level falls ‘x’dB – the amount will be specified by the machine and / or tape manufacturer. This method is called ‘overbias’ and a few dB of HF are sacrificed in the name of Low Frequency (LF) punch and low distortion. The HF loss is made up via the HF record level adjustment.
- American EQ standard is NAB for 15IPS and AES for 30 IPS.
- Euro EQ is called either CCIR (seventies) or IEC
- European EQ hides noise better.
Good luck, and may the Electron Goddess bless your tweaker.