Analog tape noob: explanation needed 2012-08-18 21:00:52 I am an audio restoration technician who already digitized over 1000 open reel tapes, the studio has Otari MTR-15 and Studer A810, and some other Studer and Revox machines. However, the maintenance of machines are done by (old) technicians from another company and I never know their "secrets". I searched terms like bias, MRL tapes, ips but I am not sure that what I read are correct or not. My questions are listed below:1. BiasMost websites/wikipedia etc says bias is a high frequency signal (over 100khz?) added in recording to improve sound quality. Then I immediately thought about noise-shaping in digital audio. However, noise-shaping is spreading noise in high frequency range (15khz-22khz in 44.1khz sampling rate, for example) but bias (from what I understand) is like a single high amplitude sine wave. Will the bias signal cause audible intermodulation distortion? Will the tape machine filter high frequency in playback mode? If I turn the reel very very slowly, can I hear the bias signal? (actually I've tried but I can hear nothing). What I really like to see is the FFT analysis of tape signal, however the recording interface in the studio only supports up to 96khz so it may not be able to record the bias signal.2. Tape speed vs playback amplitudeWe are required to set the playback level to -4dBVU when the tape is playing the test tone before the audio starts. Some tapes are recorded in 1.875 ips but the machines only support as low as 3.75 ips. I suggested to record at 96khz (we normally use 48khz) in 3.75 ips then change the playback rate to 48khz, but my supervisor said If I want to do this, then I need to set the playback level to -8dBVU because the slower the speed, the higher the amplitude. Is this correct? At least in digital audio, playback rate will not affect amplitude, it is quite strange to me.3. CCIR vs NABCCIR sounds brighter than NAB. Their differences are similar to playback EQ in cassette players. However, only type 2 (CrO2) and type 4 (metal) tapes should use the darker playback EQ while type 1 tapes should use the brighter EQ. Is this true for open reel tapes as well? I mean, some (cheap) tapes should record and play using CCIR, some (expensive) tapes should use NAB? Or all tapes can use either CCIR or NAB?Thank you very much!!