Compiler/TMS320C5505: AGC Input Parameter

Hi Charitha,

Welcome to the E2E forums. This question sounds better suited for the AIC3204 team, so I will move this thread over to that forum: e2e.ti.com/.../64

If you have any C5000 questions, please create another post under the C5000 forum:
e2e.ti.com/.../109

See this thread that shows the AIC3204 EVM GUI config tool
e2e.ti.com/.../268902

You can download that tool from ti.com
TLV320AIC3204EVM - Graphical User Interface (GUI) Software (v1.2.1) (Rev. B)
- www.ti.com/.../sloc128
- from TLV320AIC3204EVM tool page: www.ti.com/.../tlv320aic3204evm-k
- may require the EVM to use (I have asked)

Hope this helps,
Mark

Charitha,

Please take a look at this application note.  It is a little old and references some older devices,  but the AGC is almost identical from a functionality standpoint.

The reference level is full scale which is .5Vrms or roughly 707Vpk  on the AIC3204.  

I"m not sure I understand your question about getting the AGC level between +20dB to +80dB.  can you explain what you mean?

best regards, 

-Steve wilson

Hi Steve Wilson

Thank for your reply.

In that reference datasheet( www.ti.com/.../slaa260.pdf) , given as below

Noise threshold : A level or threshold for AGC to distinguish noise from a small signal, so that noise lower Variables than the threshold cannot be amplified. For the AGC, a signal lower than the noise threshold is considered as noise, and a signal higher than the noise threshold it considered to be the signal or normal.

Requirements:
The input signal SNR values are +20dB to +80dB .
The AGC should allow more than 20dB signals only and the signal which is greater that 80 dB should come to 0 dB level. Like this minimum and maximum Level How can we give ?
Is there any option to limit the Input signal? (or) Is there any Constant AGC minimum and Max values to take by itself of input signal?

In AIC3204 datasheet Noise threshold values in between -30 dBTO -90 dB(Negative values) But my Range is +20dB to +80dB .

Best Regards,
Charitha

Charitha,

I believe this may be an issue of reference point. The noise threshold is negative, because it is with respect to full-scale input. ie. if a full-scale input signal = 0dB. then you can set the noise threshold at 30 to 90 dB below that.

So when we talk about noise threshold it is the noise with respect to the full-scale input.
When we talk about SNR it is the full scale input with respect to the noise.

Do you have an EVM for the TLV320AIC3204? The AGC makes more sense when you experiment more with it.

best regards,
-Steve Wilson

Steve Wilson,

Thank you so much for your reply and valuable information. I got clarity on this.

Yes ,we are having EVM for TLV320AIC3204. I will check with that.

EX : AGC has to allow the signal between 20 dB to 80 dB
If we give input signal as 120 dB (high level).
Is AGC has to decrease that to 80 dB signal or 0 dB signal ?
May I know inside operation of AGC (Hardware Wise) ,Because software wise I am not implementing any algorithm to act as AGC.
I am just enabling Hardware AGC .
If I want to implement AGC Algorithm ,Can you suggest which will be the Best algorithm so that I can implement.


Best Regards,
Charitha.

Charitha,

"AGC has to allow the signal between 20 dB to 80 dB" - please explain this.
"If we give input signal as 120 dB (high level)" can you give me this input signal either in Volts, or in reference to 0dB = full scale input = .5Vrms?

The application note I linked to in my first response was a reference for the hardware AGC.

best regards,
-Steve Wilson

Hi  Steve Wilson,

Thanks for your reply.

In the following image input level is upto 5.3 dBu only they gave .

why target level will be -5.5dB?

More than -5.5dB why we wont have ,Is there any specific reason?

at finally Gain is  -5.1dB .

 Normally what is the range of input signal we will maintain for AGC?

why we didn't use more than +5.3dB?

If I give input signal range as +20dBu to +80 dBu What will be the output level?

Can you explain relation between Vrms and dBu ?Which has to be consider for AIC3204?

Please give me suggestions for above cases.

Thank you so much in advance.

Best Regards,

Charitha.

Charitha, 

take a look at this page.  It might help you with the dB,dBu,dBr,etc... 

+20dBu is almost 8 Vrms.  and +80dBu is like 8000 Vrms.   I imagine that's not what you're going for. 

 you don't need dBu to understand the AGC in the TLV320AIC3204, you just need to understand that the threshold for is in dB with respect to fullscale. 

best regards, 

-Steve Wilson 

Hi Steve Wilson ,

Thanks for your support and helping.

Actually if Sound level of signal  will be high means AGC will clip the information So Up to 0 dB signal only signal  level will be normal .If the signal level is more than that means automatically signal will exceeds reference level  so clipping may occur .

As shown in image signal range will be. Normally  for cochlear implants maximum range upto 80 dB  signal only.

Human can able to hear 20dB to 80 dB level only .How can I match this level with AGC interms of Vrms?

If AGC allow the signal range between 20dB to 80 dB means 7.7Vrms to 7777.7Vrms.But in our case reference level is 0.7Vrms.so the range already exceeded the reference level so all the usual information is going to be clipped .So no Use of AGC .How can we overcome this ?

Is there any compression technique inside AGC ?

The signal if it is exceeding reference level ,whether it will clip?  or it will suppress?

What is range of signls speech processor will allow interms of dB?

  

I am setting Noise threshold as -80dB

Max PGA gain 21.5

Target level =-5.5dB

attack time-1.4ms

decay time

The following are the Observation:

Figure 1:

Input signal in Amplitude

Figure 2:

Input signal in dB

Figure 3:

Output signal in dB

Figure 4:

Output signal in Amplitude

Is AGC is working fone as per above images?

I am new to AGC . Please help me out to get clarity  .Only one channel I am enabling in my case Left channel is enough.So I am using only one.

Thank you so much in advance.

Best Regards

Charitha.

Charitha, 

The basics of the AGC are that the AGC will attempt to achieve the target level at all times.  thus, if your maximum gain is set to 59.5 dB  if there is no signal present,  the gain will be 59.5dB.   this would be very noisy, so the noise gate allows the user to set a level threshold such that any signal lower than that level will be turned off. 

If the target level is exceeded,  the AGC will reduce the PGA gain to avoid clipping,  however, it is limited by the amount of gain provided.  

"Human can able to hear 20dB to 80 dB level only .How can I match this level with AGC interms of Vrms?

If AGC allow the signal range between 20dB to 80 dB means 7.7Vrms to 7777.7Vrms.But in our case reference level is 0.7Vrms.so the range already exceeded the reference level so all the usual information is going to be clipped .So no Use of AGC .How can we overcome this ?

What is range of signls speech processor will allow interms of dB?"

I'm sorry to confuse you.  I was trying to point out that you and I are using different points of reference.  So when you are talking about 20dB to 80dB you are talking SPL.  correct?  This is not what your AGC is using for a reference.  it doesn't know what the SPL is. there is an intermediate step between SPL and your AGC. That is your microphone.

Your microphone is is a transducer, its is converting SPL to Voltage. depending on the type of microphone and circuit used, etc... a given SPL will translate to a voltage level.   The AGC references thresholds to 0.5Vrms = 0dB.    so if the output of your microphone at a given point is 0.031V,  then it is -30dB from full scale. right?  (20 Log (.031/.5) ) then if you set your target level at -8dB,  and your maximum gain at 20dB, then what you will end up with is a -10dB signal.  does that make sense?

if your SPL range is 20-80dB,  what is the voltage range on the output of your microphone?

best regards,

-Steve Wilson

Hello Charitha, I wanted to check back in with you to see if you still have questions about this.

best regards,
-STeve Wilson

Hi Steve Wilson,

Thanks for your reply.

Now I understood what actually AGC will do .But I having doubts What operations basically will happen inside mic to convert SPL to voltage.

• when you are talking about 20dB to 80dB you are talking SPL.  correct? 

              Yes ,I am talking SPL range between 20dB to 80 dB

Information given about microphone in datasheet.How can I match this to voltage level.

Input Impedance: 32 Ohms

            How can I calculate the output level of a microphone? Please help me .

Thanks in  advance.

Charitha,

What microphone are you using? can you link to a datasheet?
-Steve

Steve-Wilson,
sorry ,the datasheet is not available in website.

We are using microphone- Logitech H110 stereo -headset

www.logitech.com/.../stereo-headset-h110



Please do the needful.



Regards,

Charitha

I will see what I can do.

-steve