[LAU] Re: How to analyse and "optimise" a frequency spectrum? (digitising tapes)

A side note to this discussion. Over a period of time recently I embarked on a project to digitise a large volume of cassette  tapes of live recordings of bands and other acts for which I did FOH mix. The oldest was from 1984! I found the quality of the tape was the most important factor. Chromium dioxide tapes like TDK SA and particularly SA-X survived surprisingly well, whereas iron oxide tapes much less so with severely degraded high frequency content. For some of the iron oxide tapes, I found recording with Dolby off, even if it was on for original recording, then removing the added noise later could extract a small high frequency improvement. A few went straight in the bin though. Dolby can be fickle though particularly when playing back in a deck different from the original recorder if the heads and bias haven't been optimised. I recorded the tapes to at least 24 bit wav files prior to processing, and as a last step used sox to resample to the desired bit depth and sample rate. I ran the most restorable recordings through Izotope RX (on Windows) to remove most of the tape hiss with quite listenable results. I don't know of a Linux program which can equal RX, and certainly no CLI program. Maybe noise-repellent is close but I'm not experienced with it. For consistent levels there is normalize-audio, a CLI program which can losslessy adjust to a user-defined level or IIRC the default is -1dB. Cheers, Roger