Mainly the source data behind what forms its unique graceful ‘M’ shape.
And why is Audacity 2.0.6 RIAA curve slightly different from 2.1.3 specifically in that 2.1.3’s highs section to the right of 1000Hz is flat and linear (no nodes) all the way to 20Khz and 2.0.6’s has a downward slight curved slope? I’m on a 2010 Mac Mini in OS 10.6.8.
I’ve recently acquired a curiosity about this curve after several failed go rounds EQ’ing Peter Gabriel’s “Big Time” song I bought on CD several years back but never played because it was so uncomfortable to listen to even on headphones due to its shrill and small sound with harsh overly punchy kick drum/bass and ear piercing highs from snair drum hits and Peter’s ‘S’ sounds.
I made a huge headway in sound quality improvement by just applying this RIAA curve to a duplicate waveform in Audacity and db Gain blend mixing to the untouched shrill original to taste. The results were so profoundly effective that I now had something to work with.
As a digital imaging processor and photographer it was an effect similar to when I first learned about color spaces and their importance when I scanned a photo and viewed the dark and colorless image caused by viewing within the scanner’s linear machine space in a gamma encoded display and after assigning its descriptor color space profile the image brightened up and color looked like the original photo.
The RIAA curve was like changing the sound space of the entire music file. It was amazing to see this happen and so I was wondering how its unique shape came about. I realize it’s a curve shape to cut sound waves onto vinyl that reduces the bass and increases highs but the ‘M’ shape suggests there’s more to what it’s correcting for.
I vaguely recall that the default RIAA curve was changed a long time ago (perhaps about 10 years ago?). If I recall correctly, the change was fairly minor, and was by calculating the EQ Curve points from the RIAA specification, rather than by visually copying the curve.
I think that some old versions of Audacity included more alternative curves for vinyl. Many curves are still available. Lots of information here:
Thanks, steve, for the feedback and informative RIAA curve Wiki links.
And you’re right. They’re the same curve but 2.1.3 has no nodes on highs with the last one at 2500Hz. I can drag down/up the 20kHz node end point in a linear fashion which is preferable.
I’ve been getting bug reports in Audacity 2.1.3 crashing when accessing the RIAA curve in Equalization effect where it just showed a flat line. I noted the 2.2.0 advice to switch to Graphic mode but that didn’t help. It still crashed.
I even opened the xml file (similar to the doc on your 2010 RIAA link) in Mac’s TextEdit to check for any off character which really didn’t tell me anything so I tossed all of my custom EQ curves within Audacity’s EQ effect and with the addition of just yesterday shutting down my Mac Mini and unplugging it from the wall due to thunderstorms has now allowed me to access this RIAA curve and edit it v2.1.3 without any crashing. Just tossing the custom curves didn’t immediately fix the problem but it did allow me to select “Unamed” and custom draw the RIAA curve from a v2.0.6 screenshot. I applied that to some files and now today after the shutdown/unplug I can select the RIAA filter in v2.1.3, no crashing and I can edit it. Now I’m not sure what fixed what.
So I take it from the wiki RIAA curve history & Audacity link on the subject that the arc shape of the roll off was all constructed back in the day by ear, not from knowledge of the electrical mechanics of each turntable. There was a lot of tweaking of this curve throughout its history and all at the discretion of what the label’s recording engineer “heard” at varying times throughout its history.