[LG V30 Questions & Answers] TheDannemand:
Sorry, I am bit late to this party.

[MENTION=5631635]BROKEN1981[/MENTION] is right, the ESS 9218P DAC is engaged and active anytime headphones/earphones/IEMs/powered speakers/external amp are plugged into the 3.5mm port AND the On/Off toggle is enabled on the Hi-Fi Quad DAC settings page.

I can understand the confusion: There is a stubborn myth going around that the ESS DAC is only used (or only fully active) when >50ohm headset is plugged in. So stubborn in fact, that probably a majority believe it. But it is a myth nevertheless.

This is not a matter of opinion, but an absolute fact. And yes, I have read every single post in the V30/V40/G7/G8/V50 threads on head-fi.org, along with most of the V20 ones and the related threads. Made quite a few posts there myself. I also extensively studied the ESS drivers included in the kernels of the V30, V35, V40 and G7.

As is well known, the ESS DAC does indeed deliver different levels of amplification depending on the impedance of the plugged-in headset: <50ohm triggers Normal Mode (also called HiFi mode), >50ohm triggers High-Impedance Mode, >600ohm triggers Aux mode. But ALL of these modes use the ESS DAC, just with different levels of amplification.

The easiest way to ascertain this is to simply toggle the QuadDAC On/Off with a decent <50ohm headset plugged in, and you will clearly hear the difference. If you DON'T, there is something wrong with the phone, causing the DAC to not be activated. I've had this happen, and rebooting the phone fixed it. If it doesn't fix it in your case, you have defect hardware -- or your hearing may not be as good as it once was.

For the more skeptical, there are a number of measurements posted on head-fi showing that the different modes have no effect on frequency response, as long as audible volume is set to the same level.

But for those looking for further evidence, check the following snippet from the ESS driver source code:

static int es9218p_sabre_amp_start(struct i2c_client *client, int headset)
{
int ret = 0;

//NOTE GPIO2 must already be HIGH as part of standby2lpb
#ifdef CONFIG_MACH_MSM8998_JOAN
//if(!g_dop_flag)
es9218_hph_switch_gpio_L();
#endif /* CONFIG_MACH_MSM8998_JOAN */

switch(headset) {
case 1:
// normal
//
// Low impedance 50RZ or less headphone detected
// Use HiFi1 amplifier mode
//
pr_notice("%s() : 1 valid headset = %d changing to hifi1.\n", __func__, g_headset_type);
es9218p_sabre_lpb2hifione();
break;

case 2:
// advanced
//
// High impedance >50RZ - <600RZ headphone detected (64RZ or 300RZ for example)
// Use HiFi2 amplifier mode
//
pr_notice("%s() : 2 valid headset = %d changing to hifi2.\n", __func__, g_headset_type);
es9218p_sabre_lpb2hifitwo();
break;

case 3:
// aux
//
// High impedance >600RZ line-out detected
// Use HiFi1 amplifier mode
//
pr_notice("%s() : 3 valid headset = %d changing to hifi1.\n", __func__, g_headset_type);
es9218p_sabre_lpb2hifione();
break;

default :
pr_err("%s() : Unknown headset = %d \n", __func__, headset);
ret = 1;
break;
}

The DAC itself actually only has TWO amplification modes, not THREE: Hifi1 providing up to 1Vrms (used by Normal mode <50ohm) and Hifi2 providing up to 2Vrms (used by HIM >50ohm). Aux mode (>600ohm) is implemented by the driver as HiFi1 (1Vrms) but with higher volume than Normal mode, using the Analog Volume Control (AVC) of the amp.

There is speculation that the ESS DAC activates different number of its internal DAC units as a means of delivering the increased power in HIM mode rather than simply jacking up the OpAmp (which would increase noise). I find that plausible, as described in this head-fi post. But that is far from certain, and nobody other than ESS and their licensees know for sure.

However, what IS important is that EVEN if the QuadDAC varies the number of internal DAC units in use, it does so in order to increase output power, NOT as a means of delivering "better music". Each DAC unit works exactly the same, and the number of units do not affect frequency response. It would affect SNR, but since noise is already infinitesimal on this DAC, the difference would only be audible on hard-to-drive headsets which would otherwise require a lot of amplification by the OpAmp. Multiplying the current from multiple DAC units in HIM mode would require less amplification by the OpAmp to deliver the same output power. That's all.

But as for the QuadDAC not being active or not being fully used when <50ohm headsets are plugged in, that really, REALLY is just a myth. It delivers excellent sound quality in all three amplification modes.

The only times anybody should trick the QuadDAC into a higher mode, is if their headset requires more power than the default mode can deliver. The most common example is Planar Magnetic driver headsets, which have low impedance but still require a lot of power. Highly sensitive IEMs (such as ones with Balanced Armature drivers) do not objectively benefit from the DAC being tricked into HIM.

That said, if somebody prefers something over something else, they are of course free to choose that which they prefer :)