I’ve already mentioned that my great passion is analogue music playback and records in particular. If you take a closer look, you will realise that the signal has to be filtered before it can be cut into a master lath. Low frequencies are attenuated and high frequencies are boosted in order to achieve roughly equal levels. This is usually referred to as an inverse RIAA filter. During playback, a corresponding reciprocal RIAA filter is applied in order to achieve a straight frequency response. The following article was written back in 2018, when Sowter helped me build an LCR-RIAA filter with twice the impedance of the usual 600 Ohm modules. At that time, Sowter still offered a custom design service.
The development process, theoretical principles and practical tips were summarized in a white paper and Brian Sowter published the white paper on his web site:
https://www.sowter.co.uk/pdf/LCR-RIAA%20Ahlswede.pdf
I didn’t have my own website back then. I would therefore like to publish the topic again in this article.