1). Using the USB gain knob on the Zphono: I can monitor clipping from the Zphono. Audacity also has a recording input level- but i’m confused which one to use? Do they work in tandem? If so, how to get loudest recording volume and avoid clipping?
If it has one, use the analog gain control on your interface. With digital recording, clipping occurs when the analog-to-digital converter “tries” to go over 0dB. Reducing the digital recording level in Audacity can’t help with that. Just set Audacity to maximum.
With digital recording, it’s not necessary to go as loud as possible without clipping. Peaks between -3 and -6dB are ideal. It doesn’t hurt to get closer to 0dB, but it’s usually best to leave some headroom for unexpected peaks. The important thing is to avoid “trying” to go over 0dB because the ADC is absolutely hard-limited to 0dB and it will clip. Pros usually record at -12 to -18dB (with low-noise 24-bit ADCs). It’s not like the old analog tape days where you needed to maximize the signal-to-noise ratio to overcome tape hiss.
- After my first recording, I removes pops/clicks then used the normalize effect with the recommended audacity settings. The wav file I made was really quite, so i used the amplifier effect. The recording was very good after that, but i feel i lost some of the drum slam of the original version.
It’s possible that you affected the drum sound when you removed clicks & pops, depending on how that was done.
As long as you don’t boost the level into clipping, digital amplification does nothing to the sound except amplify it.
Normalization is simply a volume adjustment, so It doesn’t make sense to amplify after normalizing (unless you’ve changed your mind about your chosen normalization level.) I usually use the Amplify effect to normalize the peaks to 0dB. (The Normalize effect also allows you to optionally remove DC offset or normalize the left & right channels independently.)
Older recordings may have more dynamic range than modern (highly dynamically compressed) CDs, so the older recording may not sound as loud even though both recordings are maximized/normalized. And, the LP production and playback process can make the recording quieter… The process (including RIAA recording & playback equalization) can act as an all-pass filter and this can make some peaks higher and some peaks lower. These short-term peaks don’t affect “loudness” or perceived dynamic range but the higher peaks will give you a greater measured dynamic range (peak-to-average ratio), and with equal peaks and a lower average the LP will sound quieter.
You can use dynamic compression (Compressor effect) or limiting (Limiter effect) to boost the volume beyond maximizing/normalizing, but of course this will affect the dynamics of the music. (Perfect, if you like that modern-boring, constantly-loud, sound! 
)
Any advice with the Audacity effects?
I usually try some “regular” Noise Reduction for the constant background noise. Sometimes there are artifacts (side effects) so sometimes I have to decide if “the cure is worse than the disease”.
Many older LPs sound a little “dull” so sometimes I’ll add +3dB to +6dB of high-end boost with the Equalizer.
Before any of that, I start with [u]Wave Repair[/u] ($30 USD) to remove clicks and pops. It does an audibly perfect job on most vinyl defects (with a choice of repair methods) and in the manual mode it only “touches” the audio where you identify a defect. However, it usually takes me a full weekend to clean-up the recording and I’m going to try something more automated next time. [u]This page[/u] (written by the developer of Wave Repair) has several other software suggestions as well as a ton of other information about digitizing LPs.
After I’m done with all other processing I Amplify (normalize) for 0dB peaks. (I do this with the songs combined in one big WAV file so the relative volume between songs is not changed.)
This is so awesome to be able to get some of my vinyl onto CD for car/archival. I’d appreciate any advice. Thank you.
Buy the CD!!! (If it’s available.) Most of the LPs I’ve digitized are old, and although I’ve had reasonably good results with the clean-up, the digitized copies rarely sound as “clean” as a CD or MP3.