Setting Levels but Android Headunit has Shite for Output, Newb Questions

[crystalworks]

Okay so I'm finally getting back on this stereo after yet another 6+ month span of ignoring it. Will update the build thread later. But first, some questions, which I am sure are of the newb variety.

Observations:

1. At full volume, playing a -2.5db 1k sine wave I'm getting a measly 0.4v at the input of the DSP. In doing some reading it seems that these Chinesium units are notorious for low output voltage.



2. At full volume and 0db boost on the inputs in the DSP I get only 0.5v output of the DSP.



3. At full volume and +10db boost on the inputs yields 1.8v at the output of the DSP.



4. I get a solid spike at 400hz in the DSP regardless of whether or not the head unit is hooked up to it. But not always???



Questions:

So obviously the audio quality of the head unit is not great, which I was suspecting at purchase, and one of the reasons I wanted a DSP. Reading on the XDA forums it seems these units are notorious for low output voltage. On top of that, I get front and rear signals out of the RCAs on the back of the unit. Fading to the rear yields no output. This does not bother me as I can do all the alignment in the DSP.

1. I am waiting for a pocket Oscope to check the cleanliness of the output signal (hopes aren't high) to determine max volume of the head unit. Assuming the Oscope reveals a clean signal at say 75%+ volume, can I boost the input levels in the DSP to compensate? I'm guessing the signal will be VERY low. At first I thought something was wrong with my DMM.

2. Assuming I can get a non-clipped, boosted output signal from the DSP (will check with Oscope), I can then set my input sensitivity on my JL Audio amps playing appropriate sine waves for the channel being set. Is that correct?

3. Is something wrong with the DSP resulting in that 400hz spike in the signal? As I said it's not always there, and sometimes I get multiple spikes at varying frequencies. It seems voltage supply dependent as the problem got MUCH better when I stuck my BMW programming power supply on the truck which supplies a solid 14v steady. My little trickle charger was being overwhelmed by the 3 JL amps which are extremely power hungry. Makes sense give the time period and quality of the amps.

Thanks for any guidance and hold holding in advance. Been doing loads of reading/watching on level/gain setting and tuning. Sometimes a bit overwhelming but I think it's soaking in. Hopefully I'll be able to figure it out without needing professional tuning. Going to order a Umik1 and use REW as it's within the budget and seems the industry standard for non-pro installers.

[89grand]

Personally, setting gains is not a big deal. Some make it seem like some complicated thing that needs to be done some precise way, but it really isn't. I never use tones or meters to do it.

A: You can't adjust the headunits output, so as long as the volume knob is not super sensitive, like way too loud with little volume level, or not enough output when turned all the way up (assuming the headunits output remains clean near maximum) then that's really all you need, so adjust the gains to achieve this. In other words, lets say a headunit goes from 0-35. I don't want the maximum system output with the volume at 20, but I also don't want to go all the way to 35 either. I'd like a volume level somewhere around 30 to be maximum for typical music, to leave some volume level for low output recordings. There really isn't any reason to want to be able to turn the volume all the way up, and still have no distortion, as you'd be leaving some output on the table. I like to be able to get a little clipping so I know the point when I'm getting maximum clean output.

B: Don't overdrive the DSP outputs by turning them to maximum. Somewhere in the middle is a decent starting point. From there, adjust the amps gains to level match the drivers for the most part. If the system sounds good, has no system noise, and has all the output you''d expect, you're pretty much good to go.

C: Once you start tuning, you will probably need to adjust some levels a bit, I'd use the DSP here for fine tuning output levels, or the amps gains if it is needed for some reason. What DSP are you using?

D: I'm not sure about the 400hz spike you're seeing. I doubt there really is a spike like that on the DSP inputs even with no source connected.

That's really it. In a nutshell, you just want the headunits volume control to be as usable as possible as far as volume level range, and if there is no system hiss or other system noise, then the gains are fine where ever they are. Since we listen to music, and not tones, tones are of no value when setting the gains. I also would save the money on the o-scope, you don't need one. Think of the volume knob as your gas peddle. Think of gains as being how sensitive the gas pedal is. You don't want the car taking off like you floored it when you push the pedal down 1" (gains too high), but you also don't want to floor it, and not get maximum acceleration (gains too low).

Turning the preamp gains up, so that you can turn the amps gains down really low is generally not of any value. Now if you have system hiss unless you turn the amps gains down, then trying turning the preamp (DSP) gains up until you lower the system noise. If you don't have system noise then don't worry about where they end up being.

[nadams5755]

some radios have a per-source level you can set as well (cd, radio, aux, usb, etc). i see it on kenwoods pretty commonly. if it exists, you could play with that as well, as long as you're not clipping the radio outputs.

some amplifiers get floor noise as gains go up. finding a balance in the radio, dsp, and amplifier gain structure can be tough.

[crystalworks]

Thanks for the responses.

Personally, setting gains is not a big deal. Some make it seem like some complicated thing that needs to be done some precise way, but it really isn't. I never use tones or meters to do it.

This is how I've always done it in the past but this being the first time doing full active and using a DSP, I figured a more scientific approach might be better.

A: You can't adjust the headunits output, so as long as the volume knob is not super sensitive, like way too loud with little volume level, or not enough output when turned all the way up (assuming the headunits output remains clean near maximum) then that's really all you need, so adjust the gains to achieve this. In other words, lets say a headunit goes from 0-35. I don't want the maximum system output with the volume at 20, but I also don't want to go all the way to 35 either. I'd like a volume level somewhere around 30 to be maximum for typical music, to leave some volume level for low output recordings. There really isn't any reason to want to be able to turn the volume all the way up, and still have no distortion, as you'd be leaving some output on the table. I like to be able to get a little clipping so I know the point when I'm getting maximum clean output.

B: Don't overdrive the DSP outputs by turning them to maximum. Somewhere in the middle is a decent starting point. From there, adjust the amps gains to level match the drivers for the most part. If the system sounds good, has no system noise, and has all the output you''d expect, you're pretty much good to go.

C: Once you start tuning, you will probably need to adjust some levels a bit, I'd use the DSP here for fine tuning output levels, or the amps gains if it is needed for some reason. What DSP are you using?

D: I'm not sure about the 400hz spike you're seeing. I doubt there really is a spike like that on the DSP inputs even with no source connected.

Turning the preamp gains up, so that you can turn the amps gains down really low is generally not of any value. Now if you have system hiss unless you turn the amps gains down, then trying turning the preamp (DSP) gains up until you lower the system noise. If you don't have system noise then don't worry about where they end up being.

Sorry, should have included the hardware in the original post. Android head unit, Audiocontrol DM-810 DSP, (x2) JL Audio 500/5, and a JL Audio 1000/1. All Stinger 4000 series RCAs. I'll give it another go with the speakers hooked up. Output was REALLY low with volume 100% on the head unit and DSP set to 0dB when listening to music. So much so I was worried something was wrong or broken. Then I checked the output voltage on the RCAs and figured the head unit just wasn't great and was hoping to compensate for that in the DSP. It sounds like I can do that, balanced with the input sensitivity on the amps, if I am gathering from your post correctly. So long as I am able to keep a clean signal.

some radios have a per-source level you can set as well (cd, radio, aux, usb, etc). i see it on kenwoods pretty commonly. if it exists, you could play with that as well, as long as you're not clipping the radio outputs.

some amplifiers get floor noise as gains go up. finding a balance in the radio, dsp, and amplifier gain structure can be tough.

Was playing from USB as the source and will check the head unit for level settings per source just in case it's present.

[Thx0849]

I had a joying head unit and yes the rca output was weak to say the least. Just go ahead and use the high level output instead, in my experience it was cleaner sounding too.

[crystalworks]

I had a joying head unit and yes the rca output was weak to say the least. Just go ahead and use the high level output instead, in my experience it was cleaner sounding too.

^That's what I was afraid of. Going to be a PITA to take everything out and wire in those speaker leads. E53 X5's (factory nav equipped ones anyway) have their radio harness in the trunk of the vehicle by the battery... which is underneath the load floor, and 3 JL amps, and the power distribution/DSP rack. This is gonna suck.

Possible bright side, hopefully I get fader back on the head unit by using the speaker wires as input to the DSP.

[Thx0849]

The effort is worth it in my opinion. The difference for me was quite noticable. Be sure to have all the timing,eq, features turned off so it doesn't affect your tune. If I recall timing was set on by default. I did decide to use the "loudness" feature in my setup though. You'll definitely be able to have fader back of you run both. If you can get your hands on a bit of "speed wire" it would make it easier to fun for sure, plus it's twisted pair and shielded!

There's a video review of a Joying like i had on YouTube and he stated that 31 was the max volume of the speaker level output without clipping.

https://youtu.be/UV9Xhfm7cTk

Hope this helps!

Sent from my Pixel 2 using Tapatalk

[crystalworks]

^Yep, apparently the newer units have better RCA pre-outs at around 1.8v-2.0v. Mine is a 2019 model and he mentions the older ones were limited to 0.5v which is right around where I am reading. So looks like I'll be taking everything out this weekend to do as you suggest. Thank you VERY much for linking that video. He was very informative and gave information on the droid units that is impossible to find anywhere else. He mentions soldering RCA leads onto the speaker outputs but since the Audiocontrol will take high level inputs I'm not going to bother. Ordered some speed wire which should arrive tomorrow. Again, appreciate the info/help.