# Pre Out Signal Level



## TNTTNT (Nov 2, 2008)

I have a Yamaha DSP-AX763, with the front L and R pre-outs connected to the line-in of my stereo amp. This is so I can use fronts for music and AV.

The volume on the stereo amp has a digital readout which can go from 0 to 79.

For a music source (CD) I need to set stereo amp at 38 for decent loudness, but with AV I have to set at 55-60 or higher. I thought line level was generally standard at 2v.

I have lifted the pre-out level by 8db (max is 10db) to try to boost, and reduced the output for speakers conected to AV amp by 8db. This means I set my stereo amp around 50, which is still high, and doesn't leave much room for adjustment.

Why is there a difference in line-in levels between CD and AV pre-outs?

Will these levels reduce the longevity of my equipment?


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## brucek (Apr 11, 2006)

> Why is there a difference in line-in levels between CD and AV pre-outs?


The CD output is not adjusted by a volume control.

Either way, no two devices output the same line-level. It's not a standard and can be quite different for different devices. That's what volume controls are for...



> Will these levels reduce the longevity of my equipment?


No.

brucek


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## thewire (Jun 28, 2007)

You might look at this link about the Loudness War if your interested in why some CD's seem so loud. Cd's are recorded louder btw.

The THX standardized system uses a fixed gain 200mV (-20dB FS) pre-amp input. That gives a 150mV pre-amp output, and 4.2V speaker output.


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## TNTTNT (Nov 2, 2008)

Thanks guys. I checked the specs, and the Yamaha's max output on Pre-out is 1v. My understanding was that many audio devices normally output 2v, although now you guys have made me aware there isn't a standard.

I hear what you are saying about the volume knob, and I am not trying to cause problems. My biggest fear is forgetting to turn the volume down from 60 to 30 when I switch to a CD, and damaging my speakers. I know I should be more careful, but accidents do happen.


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## tonyvdb (Sep 5, 2007)

I think its a different issue here, When your sending music to your external amp your probably sending just two channel and not using the surrounds. With movies the sound is split up across all 5 or 7 channels and thus the volume may seem softer. If you are only using two channels for movies are you sure you are in two channel mode (stereo) otherwise the receiver may still try to send sound to all the other channels even though they are not there reducing what you hear from the left and right speakers..


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## TNTTNT (Nov 2, 2008)

When working out 60 on the stereo amp was about level with the rest of the set up, I switched the AV amp to stereo, and took a SPL meter reading. I then switched modes so centre was active, and measure SPL on this only.

It was a bit crude, but I wanted to get the outputs roughly the same to see where my stereo amp volume was ending up.

I don't know if there is a small device which can increase the gain on small line levels, and won't change the signals in anyway. I can't build devices, although I will try to learn soon, and start with basic cabling. In the mean time, I don't know if there is such a transparent device for these situations.


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## thewire (Jun 28, 2007)

When the output line level is low, you make up for this by adjusting the volume, or trim level. There is typically source - proccessing - amplification - speakers. The amplification of the signal is best addressed in the amplification stage.


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## bluejay (Sep 10, 2007)

> I don't know if there is a small device which can increase the gain on small line levels, and won't change the signals in anyway.


I will be interested in finding the answer to this question too. It is an adjustment or tweak that a good number of people might think about. 

My guess for now would be some kind of mixer. The basic ones would not do very many small unbalanced line levels, mostly balanced microphone signals. The more advanced ones do have tons of inputs of most every description. :innocent:


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## tonyvdb (Sep 5, 2007)

Your asking to increase the signal of the input source but dont forget that almost all sources these days are digital HDMI, optical and coaxial. None of them will be easy or cost effective to boost the level outside the receivers capabilities. Analog is easy to do but not digital.


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## TNTTNT (Nov 2, 2008)

I was more thinking of boosting the line level output of the reciever, so that it was 2v into the stereo amp. I am confident that most of my other inputs into the stereo amp are 2v or close, even the turntable after phono amp.


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## TNTTNT (Nov 2, 2008)

thewire said:


> When the output line level is low, you make up for this by adjusting the volume, or trim level. There is typically source - proccessing - amplification - speakers. The amplification of the signal is best addressed in the amplification stage.



Thanks Steven. I have lowered the centre by 8db (max 10 adjustment) and raised fronts by 8db (again 10db max). This still gets me to about 50-55 on the amp, against normal level of 35-38.


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## brucek (Apr 11, 2006)

> don't know if there is a small device which can increase the gain on small line levels, and won't change the signals in anyway.


Lots of devices will accomplish the level change. The rub is, that the signal will always be degraded by a factor usually determined by price of the device.

brucek


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## audionut71 (Dec 30, 2008)

> The THX standardized system uses a fixed gain 200mV (-20dB FS) pre-amp input. That gives a 150mV pre-amp output, and 4.2V speaker output.



Wow that is interesting info, sounds like someone has THX training. I'm curious, does THX make some software available to set these levels? I have a THX cert processor and all 7 channels are THX but my sub amp is a Crown pro-sound unit that takes xlr in. Does THX specify a differing voltage level in this case (the processor has xlr outs)? I have an o-scope, is that all I'll need to dial in the proper gain setting?


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## thewire (Jun 28, 2007)

audionut71 said:


> Wow that it interesting info, sounds like someone has THX training. I'm curious, does THX make some software available to set these levels? I have a THX cert processor and all 7 channels are THX but my sub amp is a Crown pro-sound unit that takes xlr in. Does THX specify a differing voltage level in this case (the processor has xlr outs)? I have an o-scope, is that all I'll need to dial in the proper gain setting?


The Media Director which sets levels automatically intergrated into components also sets everything, crossover, eq, anything available on the device. The problem is that they have to be a partner, and THX does not have many yet, but hopefully it will pick up in the future. The device also reads meta tags based on a database or the disc, to determine what settings the creator of the media used, and sets it to that. This could also be bypassed.

To manually set levels you would need a device that reads voltage. An o-scope should work I think, :scratch: but I was recommended to use an RTA that read voltage also. The voltage level would be the same. I am only Professional level 1 and did not receive hands on training yet. There are tons of other criteria or recommendations, but that is basic setup of any type of home theater. It is more detailed than this in other words. 

We use an RTA 1/12 or better to set levels at the seating locations/location. The subwoofer is equalized and postitioned using spatial averaging. We also use the THX optimizer for quick setups.


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## audionut71 (Dec 30, 2008)

thewire said:


> To manually set levels you would need a device that reads voltage. An o-scope should work I think, :scratch: but I was recommended to use an RTA that read voltage also. The voltage level would be the same. I am only Professional level 1 and did not receive hands on training yet. There are tons of other criteria or recommendations, but that is basic setup of any type of home theater. It is more detailed than this in other words.
> 
> We use an RTA 1/12 or better to set levels at the seating locations/location. The subwoofer is equalized and postitioned using spatial averaging. We also use the THX optimizer for quick setups.


What software do you use when setting the gain levels with the rta?


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## thewire (Jun 28, 2007)

audionut71 said:


> What software do you use when setting the gain levels with the rta?


That would be a handheld RTA and simply looking at the readout, or whatever software came with it to analyize the multiple data etc. Not ever had a client before so I have not really invested much in measurement equipment. I use REW for my personal use and it has what I need anyways, at least suitable for subwoofer range since I don't have a full-range mic. My speakers go up to 24Khz so it might be interesting to try some day. I spend alot of time checking to see if it sounds right. My hearing is the most valuable tool I have.

A 1Khz sine wave at -20dB FS is 85dB for setting voltage levels.


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## audionut71 (Dec 30, 2008)

thewire said:


> T
> A 1Khz sine wave at -20dB FS is 85dB for setting voltage levels.


Even for the sub? Wouldn't the low pass on the processor kill that, or are you disconnecting the amp and just grabbing the voltage at the amp's outputs? Does software exist that sends out test tones on the LFE channel only?


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## thewire (Jun 28, 2007)

audionut71 said:


> Even for the sub? Wouldn't the low pass on the processor kill that, or are you disconnecting the amp and just grabbing the voltage at the amp's outputs? Does software exist that sends out test tones on the LFE channel only?


The LFE is automatic in the decoder, so if you set the level for the subwoofer with the crossover then you have set the LFE, at least they way I know how. If your sub is giving you the correct peaks, then you know it is working.

The subwoofer is setup differently because rooms are different. There is more to consider when placing the subwoofers but if you moved them to the correct location to give you the correct output and use the standard output voltage, this gives the correct level. The input level is -10 for the sub channel. and is fixed. Since you have the same amps as I do, that would be 150 mV in - 28X - out reference level @ 4.2V with 85dB at the money seat for your 2.1, 5.1, or 7.1, channels. The subwoofer channel is a fixed level but adjusting the gain on the subs amp does not exclude it from being THX certified if it is a THX sub. That is there for a point of reference on the intended room size for a THX setup.


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## audionut71 (Dec 30, 2008)

thewire said:


> The LFE is automatic in the decoder, so if you set the level for the subwoofer with the crossover then you have set the LFE, at least they way I know how. If your sub is giving you the correct peaks, then you know it is working.


I was not talking about setting the level within the processor. I am using a (non THX cert) Crown Xs1200 pro-sound amp to drive my sub. It uses XLR inputs that I am driving directly from my Integra DTC-9.8's XLR sub out. My concern is setting the "gain" on the amp to match the level called for in the THX spec. I am trying to figure out what the voltage level into and out of the amp should be (and how I can measure it since the XLR has 3 terminals.):help:



> The subwoofer is setup differently because rooms are different. There is more to consider when placing the subwoofers but if you moved them to the correct location to give you the correct output and use the standard output voltage, this gives the correct level. The input level is -10 for the sub channel. and is fixed. Since you have the same amps as I do, that would be 150 mV in - 28X - out reference level @ 4.2V with 85dB at the money seat for your 2.1, 5.1, or 7.1, channels. The subwoofer channel is a fixed level but adjusting the gain on the subs amp does not exclude it from being THX certified if it is a THX sub. That is there for a point of reference on the intended room size for a THX setup.


I know all about sub placement, room modes and all of that goodness, I have used True RTA to tweak the position and mix of the sub to the mains. The Marantzes that you see in my profile are driving the rear surround channels of my 7.1 setup. I am trying to get the Crown amp matched to the THX spec.

I'm a bit lost as to what you mean by the sub's input level is -10 and fixed.:huh:


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## thewire (Jun 28, 2007)

audionut71 said:


> I was not talking about setting the level within the processor. I am using a (non THX cert) Crown Xs1200 pro-sound amp to drive my sub. It uses XLR inputs that I am driving directly from my Integra DTC-9.8's XLR sub out. My concern is setting the "gain" on the amp to match the level called for in the THX spec. I am trying to figure out what the voltage level into and out of the amp should be (and how I can measure it since the XLR has 3 terminals.):help:
> 
> 
> I know all about sub placement, room modes and all of that goodness, I have used True RTA to tweak the position and mix of the sub to the mains. The Marantzes that you see in my profile are driving the rear surround channels of my 7.1 setup. I am trying to get the Crown amp matched to the THX spec.
> ...


Oh I understand now. You want the spec voltage applied to the sub. Not sure. My mono amp seemed to drive my subs about the same. It is varied on the type of sub. You might try finding a similar size driver and spec that is for a THX sub, then apply using the spec of that sub apply your gain. Sorry I'm just not certain how to do that.

I meant that the pre/out to the sub is -10. Some use -5 or 0, but THX uses -10. I thought it was what you were asking.


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