Call me stupid but I'm not getting how the sub- and sub+ outputs of the TAS5706b are meant to be used. I get a nice bass sound if I take either single one of them and apply an LPF with a ~300Hz cut-off frequency. The only difference I can see between the two is a minor phase shift.
Once and for all, which alternative below is true about the sub- and sub+ signal pair of the TAS5706b?
a) I can use either of them (doesn't matter which) and LPF thatb) I must logically AND them together and then LPF thatc) They two are differential outputs to minimize distortion and I must use a differential amplifier on them and then LPF that.d) I should do something else. If so please explain what to do and how to do it
Could someone please tell my which option is true so that I can sleep well at night :-)
Thank you very much!
STILL with the sub-woofer, eh? :)
Seriously, this is designed to be a differential signal out, but it is controlled by software (the bane of my existence...). Look at register 0x25. It depends on how you route the sub-woofer signal.
The default is ch5 to sub_pwm-, and ch6 to sub_pwm+. So, depending on how you have ch5 and 6 configured, you will get different stuff out of the sub_pwm pins.
Audio Applications Engineering Manager
Dallas, TX USA
Yep, still struggling with this and believe me, I have certainly been looking at these registers :-)
Anyway, this is an excerpt of my current config:
0x20 = 00-89-77-7A (ch6 (BTL–) to ch5—BTL pair to ch6)0x21 = 00-00-41-03 (bass management to ch6)0x25 = 01-02-13-45 (ch6 to sub+)
I take it, this means I get the desired bass-signal from the sub+ line and so I could just use that only and leave sub- floating. Correct?
Or maybe I should change register 0x21:
0x21 = 00-00-42-03 ((L'+R')/2 to ch6)
This would get me a mono-downmixed signal on sub+, correct?
The Sub+ & Sub- can be used either differentially (BTL) or in Single-Ended (SE).
If you need to use it Single-Ended (i.e. use either one of the outputs), I would recommend to make the following updates..
1.) Update Register 0x20 to set Ch-6 in AD mode (default is BD mode). AD-mode is set by toggling the Bit-D3 of register 0x20 to '0'.
2.) Update the ICD register's 0x15 & 0x16 to x04 & xFC respectively. (Default is xD0, x90).
Register 0x25 can be left at default setting for both cases (BTL/SE).
Register 0x21 can be set to either down-mix (L+R)/2 or bass-management.
Best Regards,Ravi SinghAudio Applications Engineer
Hi Ravi and thanks for answering.
I want SE mode since I'm connecting it to an external active subwoofer (i.e. a regular standalone consumer product thing).
I'll implement the mods you recommended and in the meantime, here's a couple of follow-up questions for you:
1) Does the SE-setup mean that I should use Sub-/Sub+ as signal and ground respectively or should I use Sub+ and regular ground?
2) What is the difference between a) down-mix (L+R)/2 and b) bass-management?
For the SE setup, the regular ground should be used for reference.
Down-mix is simply the L+R/2 summation, while Bass-Management is a little bit of legacy feature, that combines Ch-6 with a ratio of the other channels. The following block diagram illustrates the differnet mux options for register 0x21
Hello again Ravi,
I've tested the configuration changes you suggested and it works well.
I use the down-mix (L+R)/2 mode and take out the bass signal between sub+ and gnd which is then low pass filtered (130Hz cut-off) and then fed to an active subwoofer.
Thanks for all the help!
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