In the firmware hack thread I see repeated references to the need to disable ALC on sound.
If the GH1 has ALC, I'll eat my hat. It does have a limiter, which is an entirely different thing.
An ALC circuit is designed to increase gain in the presence of low levels of audio, and reduce it in the presence of high levels of audio, usually relatively slowly. So if you are recording in a quiet park, and a dog barks right next to you, the recorded level drops suddenly, then over several seconds it increases until the sounds of birds or whatever are very loud. If there was a lawnmower operating nearby the gain would not be raised so much as it recovered.
A limiter circuit does not attempt to increase gain. It simply briefly lowers the gain when the incoming level exceeds a certain figure. So in the example above, the sounds of nature would be heard at a lower level than if an AGC circuit was operating, and when the dog barked, the level would drop very quickly and recover very quickly, but would not be artificially raised above the normal, and the lawnmower would not cause the level to be lowered unless it was loud enough to trigger the limiter circuit.
Listening to GH1 audio and examining the waveforms I'm certain that it's a limiter not an AGC. It wouldn't be too hard to prove this with suitable test tones and if anyone thinks I'm wrong I'll do the test.
The way to defeat the limiter is to record using an externally controlled audio source (eg a mixer with a mic-level output) and set the level low enough that the limiter does not operate. That might mean recording with a level perhaps 10dB or even 12dB below the optimum, which might then expose the inherent noise levels of the GH1 audio system.
However, if using a software hack the limiter was disabled, but no level control was added, there would be no change to the way the GH1 audio sounds when recording "normal" levels of audio, but any excessive peaks would be clipped and distorted (instead of limited, as at present).
If an audio level control was provided as well as a limiter disabler, then it might be possible to control the level such that noise was avoided and clipping also avoided, but you'd probably have to be working with quite predictable audio levels with a narrow dynamic range.
All in all, I suspect that even if the firmware hack project was successful in disabling the limiter and providing level control, it would still be a poor substitute for an external low noise audio system synced to the GH1 picture in post production.
If the GH1 has ALC, I'll eat my hat. It does have a limiter, which is an entirely different thing.
An ALC circuit is designed to increase gain in the presence of low levels of audio, and reduce it in the presence of high levels of audio, usually relatively slowly. So if you are recording in a quiet park, and a dog barks right next to you, the recorded level drops suddenly, then over several seconds it increases until the sounds of birds or whatever are very loud. If there was a lawnmower operating nearby the gain would not be raised so much as it recovered.
A limiter circuit does not attempt to increase gain. It simply briefly lowers the gain when the incoming level exceeds a certain figure. So in the example above, the sounds of nature would be heard at a lower level than if an AGC circuit was operating, and when the dog barked, the level would drop very quickly and recover very quickly, but would not be artificially raised above the normal, and the lawnmower would not cause the level to be lowered unless it was loud enough to trigger the limiter circuit.
Listening to GH1 audio and examining the waveforms I'm certain that it's a limiter not an AGC. It wouldn't be too hard to prove this with suitable test tones and if anyone thinks I'm wrong I'll do the test.
The way to defeat the limiter is to record using an externally controlled audio source (eg a mixer with a mic-level output) and set the level low enough that the limiter does not operate. That might mean recording with a level perhaps 10dB or even 12dB below the optimum, which might then expose the inherent noise levels of the GH1 audio system.
However, if using a software hack the limiter was disabled, but no level control was added, there would be no change to the way the GH1 audio sounds when recording "normal" levels of audio, but any excessive peaks would be clipped and distorted (instead of limited, as at present).
If an audio level control was provided as well as a limiter disabler, then it might be possible to control the level such that noise was avoided and clipping also avoided, but you'd probably have to be working with quite predictable audio levels with a narrow dynamic range.
All in all, I suspect that even if the firmware hack project was successful in disabling the limiter and providing level control, it would still be a poor substitute for an external low noise audio system synced to the GH1 picture in post production.
