Okay. I see now the input level, in the form of blips in the left-most 5 of 15 slots. Is that enough to be useful for Audacity?
That may not be a problem. Low digital levels aren’t a problem unless they are very low,* but it an sometimes be an indication of a problem and low analog levels can be a problem.
Is the sound quality OK after running the Amplify effect?
When you run the Amplify effect, Audacity has pre-scanned the data and it will default to whatever gain is needed for normalized/maximized 0dB peaks. For example, if it defaults to +12dB, your peaks are currently -12dB. If you have to amplify by 20dB I’d be worried, but really it all comes down to the sound quality after amplifying.
The LAST thing want is to [u]clip[/u] (distort) the analog-to-digital converter built-into the turntable. None of this analog stuff is calibrated (including the records themselves) and since these USB turntables almost never have a recording level control they are usually made to record low for headroom/safety margin with “loud” records.
Would I do better by connecting the turntable to a receiver, and hook its amplified output to the Mac with a USB cable? I guess I’ll try that.
That’s an option but it’s not “just a cable”. You need an analog-to-digital converter, and there are some cables with a “soundcard chip” built-into the USB connector. Or there are USB audio interfaces such as the Behringer UCA2020 or UFO202. But the “cable” or these inexpensive little interfaces also don’t have recording level controls so you can end-up with the same problem or clipping, which is worse! Although, the headphone-output on your receiver will work and it always has a volume control.
Almost all USB turntables have line-level outputs so you don’t need a receiver or preamp (except for the volume/level control).
The old receiver I was using as a phono preamp recently died so I bought the [u]ART USB Phono Plus[/u] ($100 USD), which does have a recording level control. Or there are lots of USB audio interfaces with switchable mic/line inputs (and recording volume knobs). …I have a regular-old analog turntable, so no built-in USB and no built-in preamp.
***** If you are old enough to remember analog tape, we wanted to record “hot” to overcome the tape hiss. But with digital, no tape noise! Also analog tape soft-clips when you go “into the red” so it’s more forgiving than digital which hard-clips at exactly 0dB.