I just bought SoundMeter 1.6 (r388) for my iPhone 3G, and I'm very impressed. It seems like the best SLM app for iPhone.
I haven't delved very deeply into it today - I've just been using the iPhone's built-in mic.
I have a few first impressions about the main SLM UI in portrait orientation...
Main (large-font) digital sound level indicator.
I actually think that the display update rate is a bit too fast! It doesn't need to update any (or much) faster than once per second. I found myself immediately switching to Slow time-weighting, whatever the noise is.
Smaller digital indicators.
These are just right: great to see maximum and peak levels displayed.
I don't think that this line is even necessary. I don't know whether the area to the left of the large display is used for anything other than the 'Clip' indicator, but it seems to me that this area could be used for the indication of the quantity being measured. The indication should be as simple as LAeq, LCF etc, because the selection buttons at the foot of the screen show the full text of the weighting and response. On this part of the display, I would use Z to indicate the "Flat" frequency weighting because it seems that you really are implementing Z weighting and not just Flat weighting. If text on the iPhone doesn't allow subscripts, there could be a little graphic that showed the letters with the subscripts.
So the overall effect would be like: LAF = 72.3
Increments of 0.01 s? There's no need to have increments that are finer than 1 s. No one can control the meter to 0.01 s and the flicker of the last two digits is an unnecessary distraction for the user.
Could you put two digits in the number of seconds (e.g. 1m 07s instead of 1m 7s), please?
Beautiful! But there's no need to have a decimal place in the level labels. It would be clearer with just 20 ... 40 ... etc. It would also be nice if the quantity label here could be in the format LAF, if that's possible. Would the quantity label be better placed at the left edge of the bar graph rather than underneath? This would save all the unused space to the left and right of the quantity label. The bar graph would be narrowed slightly, but it would still have the same visual appeal.
I'm going to suggest that you could delete the labels 'Level Type:', 'Weighting:', and 'Response:'. I think that anyone willing to pay the purchase price for this app would be able to figure out what the function buttons do without the labels.
And in landscape orientation...
Similar comments to the above. Move the quantity label for the bar chart to the top or bottom of the bar chart and run it horizontally like all the rest of the text.