I got a problem here.
The book says that with PeIm spells that reduce the range of the voice of the caster, it also limits the range of the spell. For example, a spell that silences a mage will only allow him to cast voice range spells on himself.
Fine by me but what happens when you change the voice of a caster using MuIm to that of a baboon for example?
hmmm... hard one I think...
Since a magus changed into an animal can't use voice at all (as noted under Muto Corpus, I believe), the answer seems to be you can't use voice to cast spells when your voice is changed to a baboon's.
The whole "change Voice range through magic" is problematic, though. You can apparently lower the range, so can you increase it? That's exploitive.
There was a big discussion on this on the Berklist some time ago. I think the end consensus was that you shouldn't be able to, and that you can twist the rules so they come out "right".
Personally, I would be incline to make spells that change Voice range into Muto Vim spells with an Imaginem requisite and be done with it. Just changing the Imaginem itself will not affect the "magical sound" of the mage's voice... or something 
you can extend Voice range by shouting at the top of your voice.
Sp, a loud-hailer spell is going to extend Voice range further, but also alert and annoy any neighbours who can hear.
Local Faeries may be upset, magical creatures, the local Saint, priests, nobles,... nobody likes being woken from their peaceful rest by some idiot shouting magical phrases in latin, complete with imprecations and invocations of sacred (and profane!) names...
I am not sure what you are getting at. I used to teach basic training and trust me I could project my voice several hundred meters absolutly clearly and without a problem. Or try an opera singer. It is a question of learning to use your stomach muscles. Now why you think a baboon is fundamentally better than that is beyond my understanding.
"Battle Voice" is something most commanders learn in the middle ages, you need to be heard. About the only thing a baboon has is that the sound is high pitched...just the same way a female NCO has an advantage that her voice is pitched higher than a base drum and can be heard above it while a male's voice is competing with it.
Humans can be right loud when they want to be. You don't need to be a baboon. A trained orator can fill a large volume with their voice without modern loudspeakers. All it takes is training and understanding that the sound comes from your stomach not your throat/upper lungs in end effect.
That is the difference between Pat Benatar and Darby Mills...
Sorry... I guess that my intentions we not clear. The effect was not to augment the Voice range but to disturb it. Now can a baboon emit intelligible sounds ? If it can than my example was bad. Use that of a horse than or a mouse, dog, etc.
The goal is to stop a magus from incanting & render him a but ridiculous in the process.
Now would the fact that we all hear a dog barking instead of Latin prevent the spell to be casted @ voice range?
Use at Voice but without standart words so -10 of the casting total.
As I understand it William was talking about changing the Voice so that you couldn't make human sounds. I would say that is a MuCo(An) effect, but anyway.
If you can't speak, spells cast at Voice range can only affect yourself. It is also stated that magical enhancment of hte voice does not increase voice range. So that should be that.
The problem with animal voices and spellcasting is one we (in our saga) assume house Bjornaer has solved with the spell Voice for Bjornaer, in 5th I'd say this is a MuAn base 3 or 4 effect.
But that was perhaps the other way around, William eas perhaps talking about changing a magus' voice to hamper his spellcasting? Se also ReIm 25 - The Captive Voice.
We have used the the guideline that however far your voice would carry, and be understood, would be the range.
Consider: If you don't verbalize a spell, you get a penalty...I don't recall any prohibition preventing you from casting a spell on another when you do so...????? If the range of the spell is 'voice' and you did not verbalize, it should still go the same distance (your paying the penalty already)...
my $.02
Nope you were not clear. A baboon has vocal cords and can certainly "talk" I would say that "changing the voice" is impossible unless you physically change the person to an animal (or part of the person) that can't make regular words, that is MuCo(An).
If you want to effect the voice (as in people hear something else) it is a MuIm spell so that the sound comes out as something else. He talks and sounds like a dog barking. If that would affect the spell is up to the story guide, as I am not sure if the "sound" being different matters in the end.
Well, I understod him, see three post above.
Hmmm... that's interesting. If this were possible a magus could cast spells, screaming with booming voice and all that, and have a MuIm effect up that makes it sound like he is humming Tenorus the Minstrels latest, baudy hit. Would be great for magi who often travels to towns and deals with mundanes.
It's interesting and ultimately up to your story guide. It is not clear to me in the least, which way you go on this one. I can make arguments, right now, on both sides of the fence so you might want to settle it based on game balance and that would, from my viewpoint anyway, say that you can't do that.
A SG call if I have ever seen one.
This is a sticky one, isn't it? Having a limit to voice range is good, and it the reason for its place in the range magnitudes. And yet, you SHOULD logically be able to increase it. It's a tough call, to be sure.
I was contemplating this very issue when mulling over the notion of Ars Magica modern. Would it allow voice to be transmitted? Could you have range Phone, or maybe range IM? An interesting mental exercise, but ultimately bringing up more complication than I wish to deal with at the mo'.
Spontaneous magic we know is an made up on the spot, but is based the standard theories and traditions of Hermetic Magic. These theories and traditions are codefied into rote in Formulaic Magic. That is a specific action produces a specific result.
Example:
If Pillum of Fire require one to make the gesture of throwing a Pillum, this gesture occurs everytime the formulaic version is cast. If one wants to spontaneous simulate Pillum of Fire, based on what they know it is advantageous to use the gesture of throwing a Pillum. One is not obligated to, but in order to better near the formulaic version it may help.
I point this out, because even if an Ape can make sounds, maybe even understandable sounds, I do not believe an Ape can accurately mimic the specific sounds a human voice creates when casting a formulaic spell (incantations). Because of this, even if a mage were capable of making sound, I would rule that the sounds do not make up the formulaic 'gestures' of the spell. Therefore I would provide the no voice penalty. One could argue that the fluid nature of spontaneous magic is less dependant on ridgid repeatable voice and gestures. Depending on the GM, the voice penalty for having a monkey's voice while casting spontaneous magic to could be the full penalty to perhaps half.
I don't think having the voice an animal will allow one to gain a bonus or extend the range. Other magics could do this, but nothing that involves Animal.