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In previous recordings of SOASC=, I used to solder a wire between PIN 26 (SID EXTERN IN inside C64 on SID chip connection) to GND internally to ensure reduction of hiss/noise into the recordings.
However, we can achieve the same effect by simply doing this externally inside a modified AUDIO/VIDEO 5-pin DIN plug instead, by putting a wire between PIN 5 (Audio IN) and PIN 2 (GND).
In addition for max reduction, thanks to PSID64, we can even blank the screen to ensure the VIC Graphics chip also is reduced to a minimum of noise/hiss. Allthough, that would not work for BASIC tunes recorded or other wierd rips in the HVSC (where parts of the graphics are still visible) during playback, but that's only 1% or less of the collection anyway :-)
Here are the actual results of that, recorded on a Delta Audiophile 2496 PCI soundcard which are used on all SOASC= ROTS recordings to produce FLAC and MP3 recordings.
The suspected SID file for testing was converted from SID to PRG with the excellent PSID64 before recording and loaded off a MMC64. Recording was done in Adobe Audition as well as showing the Spectral View pictures below.
You can also download the same WAV recordings and see/hear for yourselves.
Note that SOASC= ROTS does nothing else to the recordings, except for a normalize volume (described in the FAQ) applied to the recordings. Everything else is just as it comes out of of a real Commodore 64 with a standard SID CHIP into real analog wires into the recording card on a separate PC nearby.
The tune selected was randomized, and came from HVSC #50, DEMOS/G-L/Holy_Shit_part_2.sid by Daniel Mannestig (Madmax), 1991, Mocean.
All of the noise/hiss reduction, including the VIC chip can be seen in the link posted at bottom of this page.
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No hardware noise reduction
Reduce noise in SID (http://codebase64.org)