Short version: Don't use them. Long version:
I had planned to film an episode to cover this because several people have asked about using the built-in effects and processing in the RODERec app. I really like this app but I don't use the processing or effects. Why? Because iOS has placed enough limitations on app developers that the processing is not all that useful.
What do I mean by that? Consider a limiter effect. Limiters are super helpful when recording because they can prevent your audio from clipping when your talent suddenly gets louder than expected. So this would be the number one effect to have in a recording app. The issue is this: For a limiter to be useful, it must do its job before the audio is converted to digital. Why? because if it is first converted to digital, the damage and clipping has already been done.
And there's where iOS has prevented RODE from allowing this effect to be useful in RODERec. Because Apple places boundaries around what apps can access and what they cannot, RODE can't access the audio before it is converted to digital. It is simply a decision that Apple made to help ensure the stability and reliability of their OS.
I don't blame either company. It is a stretch to expect that a phone would have the ability to be an amazing audio recorder.
A limiter effect would be possible with add-on products that connect to phones, as long as that add-on device did the limiting before the audio was sent to the phone.
The same applies to the other effects that one might like to apply at record time like a compressor.
I suppose things like a low cut filter might be ok to use, or the hiss reducer, but I'd rather apply that stuff in post if I must, just because I'm a little bit picky that way. I don't want to apply processing and regret it later when in post I find that it mangled my audio in some way. I'd rather apply that non-destructively in post so I can back out if I must.
And here are my original notes for the episode I was going to film:
How to improve the sound of your dialogue audio using RODERec.
Great app, the full version is priced at $5.99 USD.
Some have complained that it crashes in the reviews but I have not had that problem on my 3rd generation iPad (on iOS 6 and iOS 7), iPad Air or my iPhone 5S.
Now for the processing--I believe this is only available in the full version, not the LE version.
- Why would you want to do any processing? - The most common use case I run into is this: I'm filming talent and before we start rolling, I have them speak for a few minutes (if it is an interview) or run through a few of their lines if they are acting and set the input level or gain on my recorder. But then during the recording, the talent or actor speaks louder, their dialogue may clip--get too loud for the recorder to record which makes some pretty nasty sounding, unusable audio… - Another use case: You have a tight timeline and you don't have enough time to painstakingly edit each audio clip, at least not extensively. - In both of these cases, the built-in processing by iZotope can help. Incidentally, iZotope is a pretty well respected audio processing company in the audio space so this is a pretty awesome feature of this app. - How can the processing help?
- Using Mild Compression setting will solve one of the two problems above: - It will NOT help prevent clipping. It seems like the way this is working is that the audio is captured, clips and all, then run through the compressor. So this will not prevent clipping! You have to get your gain right before recording. - The mild compression feature can also speed up your post production workflow by taking care of evening out dialogue while you record, so you don't have to do that in post. In this case, you can pretty much just normalize the file and be on your way. If you use Premiere pro, for example, you can just right click on the audio track, choose audio gain, and then choose normalize all peaks to -0.1 db.
- What are the risks with doing this? - The compression is baked into the audio track and you can't easily uncompress it. So if you want a recording with a lot of dynamic range for whatever reason, you probably don't want to use this processing option. - Overall, I find this pretty useful and pretty low-risk but remember that you still have to watch out for clipping. In outboard analogue gear, the compressor usually manages the spikes before the recording is stored. Not so with RodeRec.
Other Presets--I don't find these useful as often, but here's what they do: - Rumble reducer - helpful if you have a lot of low frequency rumble you want to control. If this is really a problem, my first choice would be to figure out how to stop the low frequency rumble which often means recording somewhere else. - Hiss reducer - helpful cutting hiss by simply EQing out some of the sound above 10K. Same as above, if you're recording in a space with a lot of this hiss, you may be better off eliminating the source of the hiss or moving to a different place to record. - Soft Clip Limiter - Sort of like a more extreme version of the compressor. Not quite as useful because the effect is pretty imposing/noticeable when recording dialogue. More useful as a special effect. - Hard Clip Limiter - Even more extreme than the soft clip limiter. Again, not quite as useful for normal dialogue but more as a special effect, maybe for recording screamo music?
Note, you can only use one preset at a time and I find that of all of these, the mild compression preset is the most relevant and useful for speeding up your workflow when recording dialogue.