In reply to:
1) If I do get a SPL metre should I get a analogue or digital - does it matter?
2) I see the Yami can put out a test tone, is this OK or do I need a test disk?
1. It doesn't matter. Some prefer the analog; some the digital. I'm among the latter. Either will do the job.
2. The tones in the Yami will suffice. Check the Yami's manual to be sure, but most receiver's indicate their tones should be set to a level of 75 dB.
The discs, however, offer a lot more than just tones to balance your audio system, and are worthwhile if they fit the budget.
