There have already been some excellent answers, but just to try and add some further clarity...
[quote="mken"The CD I have ended up with sounds not too bad, but overall , compared to a commercial cd , the volume is lower.[/quote]
The commercial CDs format has evolved to become what is known as 'peak normalised'. What that means in practice is that a lot of music is mastered in a way that makes it squashed up against the end-stops, with peaks banging on the maximum (0dBFS) and the average levels not too far below that. So there is little dynamic range and it sounds very loud (and fatiguing, usually!)
So, if you compare your mixes with a commercial CD the chances are it will tend to sound quieter and more dynamic. Personally, I think that's a good thing... but I get that you want things to sound more comparable... and I'll come back to that in a moment.
In the meantime, it's worth noting, though, that the peak-normalisation idea is now obsolete and rapidly going out of fashion along with the physical CD format. Most music is now consumed online via streaming, and all of the main streaming services employ loudness-normalisation rather than peak-normalisation.
What that means is that each track is assessed for its average loudness (rather than peak levels), and then the track's overall replay level is turned up or down so that its loudness matches that of every other track on the system. The aim is to give the listener a consistent experience without having to continually adjust the volume between tracks.
This approach also means that there is no longer any need -- or benefit -- to cranking the level and squashing the life out of tracks to make them appear loud. Everything now has the same perceived loudness as everything else. In fact, a typical peak-normalised CD track now tends to sound what it is -- flat, dull and lifeless -- when played on a loudness-normalised platform. And the huge benefit for music lovers is loudness-normalised platforms really encourage the use of dynamics -- and a track with good dynamic range tends to really stand out and sound great!
The minor complication at the moment is that different streaming services use slightly different methods of assessing the average loudness. However, there are now formal standards recommendations and they are converging into a consensus. Already the variation between different services is only a few decibels, so it's not too hard to come up with a master that works perfectly well on all of them.
So... what I'm saying is that while you may feel the need to employ a peak-normalisation approach to try and make the CD sound as loud as typical commercial tracks, it would be worthwhile either compromising the amount of squash so that it will still sound good when played on a streaming service... and/or come up with a more dynamic loudness-normalised version specifically for uploading to the streaming services.
Anyway... back to your CD mastering situation:
Using Audacity if I use the amplify function then it will increase amplitude until a spike hits the "0 " level. Don't know if this means 0db?
I don't use Audacity but it probably means 0dBFS -- digital F
I have been thro each track and tried to reduce individual peaks which then allows me to "amplify" perhaps another 0.1 or 0.2 db and then repeat procedure knocking peaks out and reamplifying. However this is a time consuming process and I wonder if what I'm doing is in fact " limiting" the levels but manually.
You are doing precisely that! It would be quicker and easier to set up a peak limiter and shave off a decibel or two. However, I would caution against making 0dBFS your target level because that is likely to result in clipping in the reconstruction filter in the replay output. Instead, set the limiter to hold everything a little lower -- say -0.5dBFS as a reasonable compromise.
Also I wonder if each peak I reduce is actually detracting from the dynamics of the sound. I have tried both "normalise" and "compress" but feel they both produce a much more "squashed sound".
Yes, obviously reducing the transients will reduce the overall dynamics. the 'Normalise' function shouldn't affect dynamics at all. It is just a level shift to raise the maximum peak level of the entire track to a predetermined level (often 0dBFS, but possibly you can set you own level). 'Compress' is obviously a dynamic process intended to reduce the dynamic range in some way...
I believe there have been various standards over the years such that a 70's CD will not sound as loud as a current CD because of newer production techniques.
Quite so. Back in the 70s vinyl was the standard consumer format and that couldn't cope with excessively loud and compressed music -- you could have one or the other, but not both! The advent of the CD in the early 80s allowed producers to do anything they liked, and so they seized upon the long-standing idea that louder and brighter always sounds better and more exciting (at least in comparison to quieter and more neutral!)... so the 'loudness war' really took off and the peak normalisation thing got progressively more aggressive and silly.
One last question, if I take the wav files to a CD reproduction company is it likely that their process may automatically "burn" the cd at current volume levels?
No, by default they will burn whatever you give them to burn... but some may offer an in-house mastering service that could process the mixes to achieve a more commercial sounding volume. Whether they do that well or not depends on who is doing it I guess... some mastering engineers are better than others! :-)
Finally, I agree with the post above that 'parallel compression' (also sometimes referred to as London or NewYork compression) can be an effective mastering process.
This reduces the overall dynamic range to make the average level higher and so increase the perceived loudness... but whereas a conventional compressor (and limiter) works by turning down the loud bits ('top down'), parallel compression works by raising the quieter bits (bottom up).
Inherently, top-down compression/limiting does most of its work on the transient spikes, to it tends to audibly affect dynamic transients. In contrast, bottom-up compression tends to leave the transients unaffected, which -- in drum-forward music -- can sounds noticeably better.