The difference between AVC and AGC
Hi,
The block "AVC" is used.
The curve of this AVC is as follows: it follows the input with a gain of -18dB and saturates at level of 0.538Vcc (crete-to-crete).
The 0dBFS level is 1.1Vcc, so here 0.538Vcc is near 0dBFS.
I noticed that when I change the default values, the behaviour of the device does not change a lot (??).
When we need to implement an AGC , we need in fact the "reverse".
I.e. a high gain for low input signal and the circuit must saturate near to ~0dBFS so that the gain is kept ~1
We have 2 solutions: put an amplifier at the input or put an amplifier at the output.
Put an amplifier at the input channel, the gain is limited to 48dB to avoid saturation for high levels.
Put an amplifier at the output stage, here there is no saturation issue.
It is also possible to put both.
What is the good solution relative to the signal to noise ratio ?
Is there a normal configuration ? I mean the value commonly used for such a device?
Do you have experimented this circuit?
How could we test it? Of course it is not a linear circuit so a Bode curve does not make sense here.
Does it exist an official curve of the normalized voice for films Dolby5.1 ?
If you can illuminate my poor knowledge of this subject, you are the welcome.
Best regards,
Patrice
Audio Signal Processors
adau1451
hardware
SigmaDSP Audio Processors
Hi,
I put a gain of 18dB at the input and that looks good (no saturation) and the output of the circuit is always 0.613Vcc.
The dynamic is very high: I mesured from +9dB downto -72dB and the device works fine.
Hello Patrice,
We had all discussed this a while back in this earlier thread:
(+) AGC - Q&A - SigmaDSP Processors & SigmaStudio Dev. Tool - EngineerZone
I had linked to another thread where I had a program written for the 1701 that did the AGC with standard blocks. This would give you more control over how it works. So maybe translate that over to the Sigma300.
We do not have any official blocks that conform to Dolby 5.1. We used to have some ProLogic blocks and possibly some others but they were done on a SHARC and were licensed.
Dave T
Hi,
Many thanks Dave, but I purchased now an ADAU1452 board and it is what I needed. It seems the AVC works with a control loop while your device on the ADAU1701 uses a reciprocical function.
You said that the dynamic range of a loop is better, isn't it?
It looks good so I prefer to use ADAU1452 (the fact also to have 3 inputs).
Best regards,
Patrice.
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