Are there any **audible** differences? Yes, certainly but not a lot.
Keep in mind that MP3 cannot guarantee transparent compression at any bitrate. Not even at 320 kbit/s every song or sound effect will be perfectly transparent. There are some unfortunate sound combinations that just cause pretty much every MP3 encoder to fail even at 320 kbit/s.
The question is: Are there are lot of cases where the encoder will fail at 192 but not fail at 320 kbit/s? And therefor you have to take a look why an encoder can fail in the first place.
An encoder will usually not encode a signal it deems "unhearable" according to its psychoaccoustic model, no matter what the bitrate is, as that would only waste bits for nothing. The problem is: There is no perfect psychoaccoustic model in the world! All existing models have been created by making AB or ABX tests with voluntary testers and are thus only as good as the hearing capabilities of the test persons as well as the quality of the equipment used for testing. So if the model is flawed, it may throw out signals it should have kept. And even it is not flawed, it only models the average listening capabilities of the average listener. Yet there are people with listening skills far above average, too. If the model is causing the problem causing the audible difference, raising the bitrate may not help much or may not help at all, as the encoder may still throw away a signal it should have kept.
However, an encoder may also fail if it knows that a signal is hearable, yet cannot encode it as it ran out of bits. At some point the encoder has to also throw away hearable signals as the amount of signals it can store is limited because the bitrate is limited. Encoders usually try to be clever and throw away the signals that should be least noticeable to be missing but even if one of these are missing, some people may be able to notice that. And if that is the problem causing the audible difference, then of course raising the bitrate will improve the situation.
So the question is: How often does an encoder has to throw away important signals it couldn't encode at 192 and that it could have encoded just fine at 320 kbit/s?
To get an idea for the answer you can use a VBR encoder like LAME and use it as best quality (`-V 0`). At that level LAME tries its best to preserve every signal it considers hearable by human ears according to its model. So whenever a frame is encoded with less than 320 kbit/s, then no more than the bitrate of that frame was required to preserve all these signals. Here's a sample output of running such a command:
```
Encoding as 44.1 kHz j-stereo MPEG-1 Layer III VBR(q=0)
Frame | CPU time/estim | REAL time/estim | play/CPU | ETA
7800/7800 (100%)| 0:03/ 0:03| 0:04/ 0:04| 57.172x| 0:00
32 [ 1] *
40 [ 0]
48 [ 0]
56 [ 0]
64 [ 0]
80 [ 0]
96 [ 0]
112 [ 0]
128 [ 7] %
160 [ 28] %
192 [ 13] %
224 [ 829] %%%%%%%%%%%%%%%%%%%%%***
256 [4192] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%********************
320 [2730] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%***************************
-----------------------------------------------------------------------------------------------------------------------------------
kbps LR MS % long switch short %
274.4 77.1 22.9 85.2 8.0 6.8
```
As you can see, LAME was convinced that most of the time more than 192 kbit/s are required. If you had limited the MP3 to just 192 kbit/s, then most of the time hearable signals would have been dropped. Also notice that only in case of a 320 kbit/s block, LAME may have been running out of bits, as in all other cases, it could just have increased the bitrate if that was the case but apparently in some cases 256 or 224 were enough and in a few cases even 192 kbit/s were.
Note however that the example above was LAME trying to be as lossless as possible. Most people neither have ears good enough, nor equipment good enough to require such a level of quality. For the vast majority of people and home equipment, `-V 2` should be perfectly transparent. So let me repeat that test again with that option:
```
Encoding as 44.1 kHz j-stereo MPEG-1 Layer III VBR(q=2)
Frame | CPU time/estim | REAL time/estim | play/CPU | ETA
7800/7800 (100%)| 0:03/ 0:03| 0:03/ 0:03| 63.878x| 0:00
32 [ 1] *
40 [ 0]
48 [ 0]
56 [ 0]
64 [ 27] %
80 [ 17] %
96 [ 4] %
112 [ 5] %
128 [ 14] %
160 [1554] %%%%%%%%%%%%%%***********************************
192 [3849] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*************************************************************
224 [1167] %%%%%%%%%%%%%%%%*********************
256 [ 830] %%%%%%%%%*****************
320 [ 332] %%%%*******
-----------------------------------------------------------------------------------------------------------------------------------
kbps LR MS % long switch short %
201.7 41.4 58.6 85.2 8.0 6.8
```
And now you can see that to reach that level of quality, 192 kbit/s is in fact enough most of the time, often even 160 kbit/s is. There are only a few cases where LAME hat do go up to 224 and only very little where it had to go all the way up to 320 kbit/s.
One of the difference between `-V 0` and `-V 2` is that the first one considers all frequencies as important whereas the later one only frequencies below **18671 Hz**, which is one of the reason why it has to encode less signals. Yes, human beings can hear ut