How to volume adjust?

[richoval]

Hi guys, can someone explain to me how to volume adjust properly? I have 2 DAPs and I wanna compare them, how can I figure out the volume level on each DAP with one specific IEM? Thanx for your help! Cheers

 

[castleofargh]

one possible solution with a cellphone:
You could start by setting the listening level to you preference on one DAP, then put your IEM on a table with the nozzle right against the mic of your cellphone using some SPL meter app of sort(needs to show one decimal value to be of use). You play some test tone or maybe white noise and check that you can get a consistent result that is higher than ambient noise floor(to be sure the IEM is close enough and loud enough for the cellphone to pick it up). The easy fix if that doesn't work is to increase the volume of the DAP, but then you're going to be stuck testing the sound at that increased loudness, which is really not ideal for subjective impressions. So you might end up spending most of your time figuring out a way to have the IEM really on the mic in a steady enough way, with the nozzle really being stuck onto the mic's hole, or just trying to find a quiet enough room or a more sensitive recording source.
Then assuming you're all set, you just unplug the DAP(again not moving the IEM at all!), and you play the same test signal in that second DAP while adjusting the volume to get the measured level you had on the first DAP.
you can do that back and forth a few times to confirm that the IEM and cellphone didn't move and your measure is correct.


Now for the problems with that approach:
- Your DAPs might not offer small enough increments to set the volume level you need. So you might have to repeat the process a bunch of times to find a moment where both DAPs happen to fall really close with their respective volume system(ideally within 0.1dB).
- Depending on the IEM, the impedance difference between the DAPs could cause a change in frequency response of the IEM. Depending on the magnitude of the change and where in the frequency range, your test signal might not represent the overall change or subjective perception of loudness(like if 1kHz is boosted but the rest goes down and you measure a 1kHz tone...). If the frequency changes significantly then the very notion of level match becomes a complicated question. One I don't know the answer to. I have some ideas but at some point, a different sound is just that.

edit: I mentioned using noise, thinking it could help in case the amplitude of a tone wouldn't be enough, but it brings a different issue as @VNandor mentioned, so let's not.

 

[richoval]

That sounds like a pragmatic way to do it, i‘ll definitely try that. To be honest, i thought there must be some kind of equation, since the only variable with the same IEM seems to be the power applied through the output of the DAPs or is that to simple minded?

 

[bigshot]

I bought a pair of identical used preamps on eBay. They have nice big volume pots. I use them to level match. But you can do it with a single one and match one DAP to the level of the other if the preamp is transparent (most of them are).

 

[castleofargh]

That sounds like a pragmatic way to do it, i‘ll definitely try that. To be honest, i thought there must be some kind of equation, since the only variable with the same IEM seems to be the power applied through the output of the DAPs or is that to simple minded?

If you know the voltage into the IEM(or have a way to know what the voltage output of the DAP will be into a given load), you can certainly calculate most things as accurately as your data is accurate. The problem is to know what will come out of the DAP at a given volume setting. We typically won't know that. And if you turn down the volume on a DAP by one unit, what does it means in voltage? That one unit has probably nothing to do with one unit on the other DAP anyway. Rapidly you find out that if you rely on measurments you need them all or you must measure those you need yourself.
Plus I assumed that you could sooner find a cellphone or some earbuds with a mic, than a good multimeter for audio range and low voltage, and the right plugs and adapters to measure voltage while the IEM is plugged in(or using a similar load).
TBH, I can do both options when I have to check something like an IEM's sensi, and I almost never bother with the multimeter beside when I'm checking that my calibration is ok. I happen to have a bunch of cheap artificial ear couplers and mics to measure IEMS, so obviously it's much easier and consistent for me than sitting the IEM near the cellphone's mic as best as I can, but the general idea is the same.

 

[richoval]

guys, thank you very much for your input, very helpful!

 

[Redcarmoose]

one possible solution with a cellphone:
You could start by setting the listening level to you preference on one DAP, then put your IEM on a table with the nozzle right against the mic of your cellphone using some SPL meter app of sort(needs to show one decimal value to be of use). You play some test tone or maybe white noise and check that you can get a consistent result that is higher than ambient noise floor(to be sure the IEM is close enough and loud enough for the cellphone to pick it up). The easy fix if that doesn't work is to increase the volume of the DAP, but then you're going to be stuck testing the sound at that increased loudness, which is really not ideal for subjective impressions. So you might end up spending most of your time figuring out a way to have the IEM really on the mic in a steady enough way, with the nozzle really being stuck onto the mic's hole, or just trying to find a quiet enough room or a more sensitive recording source.
Then assuming you're all set, you just unplug the DAP(again not moving the IEM at all!), and you play the same test signal in that second DAP while adjusting the volume to get the measured level you had on the first DAP.
you can do that back and forth a few times to confirm that the IEM and cellphone didn't move and your measure is correct.


Now for the problems with that approach:
- Your DAPs might not offer small enough increments to set the volume level you need. So you might have to repeat the process a bunch of times to find a moment where both DAPs happen to fall really close with their respective volume system(ideally within 0.1dB).
- Depending on the IEM, the impedance difference between the DAPs could cause a change in frequency response of the IEM. Depending on the magnitude of the change and where in the frequency range, your test signal might not represent the overall change or subjective perception of loudness(like if 1kHz is boosted but the rest goes down and you measure a 1kHz tone...). If the frequency changes significantly then the very notion of level match becomes a complicated question. One I don't know the answer to. I have some ideas but at some point, a different sound is just that.

Such a great post!

 

[richoval]

Ok so I gave it a shot like this:

Set up:
- AK SP2K and SR25
- EE Odin
- Decibel X App on my iPhone
- white noise downloaded from here: https://mc2method.org/white-noise/ ("motor" and "vacuum")

1. played some tunes on my SP2K and set volume to my preference (45 on balanced)
2. playing "vacuum" and holding the IEM to my phone (placed the nozzle in front of the mic where the loudest measure is) -> dB Meter reads +/- 80dB (was impossible to correctly adjust it to 0.1, to be honest, it was already difficult without the decimal increments, should I use cleaner sound?)
3. swap to my SR25 without changing position of the set up with the IEM and adjusting volume until I get +/-80dB -> 53 on balanced
4. check both players with the same setting but playing "motor" -> same dB measured (+/-70)

Somebody detecting any obvious mistake? Should I use different sound-samples? Should these volumes work with any other IEM as well or would I need to repeat these steps?

 

[VNandor]

I have no idea why anyone would recommend using white noise for volume matching DAPs, maybe @castleofargh will care to explain it? I think using a sine wave your mic can reliably pick up (so anything between 200Hz~2kHz is a good bet) is much easier to handle and just as accurate as using white noise in this case but I wouldn't use a microphone for volume matching DAPs in the first place anyways.

Probably the most accurate and complicated thing you could do is to use a multimeter if you or maybe someone you know has one, set it to measure AC voltage and measure the output voltage of your DAPs while using your headphones as a load. If you know what any of this means, you probably wouldn't ask for advice though.

If you happen to have a computer that's connected to an analog audio input like microphone inputs, or line inputs, you could just connect the output of your dap to that and record you input with some software (like Audacity for example) and match the levels using that. Just make sure you don't blow up your inputs by using too high volumes. This shouldn't be too hard to do and I think it's gotta be at least as accurate as trying to record the actual sound level of the IEMs with some microphone.

 

[richoval]

I have no idea why anyone would recommend using white noise for volume matching DAPs, maybe @castleofargh will care to explain it? I think using a sine wave your mic can reliably pick up (so anything between 200Hz~2kHz is a good bet) is much easier to handle and just as accurate as using white noise in this case but I wouldn't use a microphone for volume matching DAPs in the first place anyways.

Probably the most accurate and complicated thing you could do is to use a multimeter if you or maybe someone you know has one, set it to measure AC voltage and measure the output voltage of your DAPs while using your headphones as a load. If you know what any of this means, you probably wouldn't ask for advice though.

If you happen to have a computer that's connected to an analog audio input like microphone inputs, or line inputs, you could just connect the output of your dap to that and record you input with some software (like Audacity for example) and match the levels using that. Just make sure you don't blow up your inputs by using too high volumes. This shouldn't be too hard to do and I think it's gotta be at least as accurate as trying to record the actual sound level of the IEMs with some microphone.

thank you for your input. I‘ll have to check with some friends if somebody happens to have a multimeter, probably not though... but surely somebody has a computer with an line input.

 

[VNandor]

thank you for your input. I‘ll have to check with some friends if somebody happens to have a multimeter, probably not though... but surely somebody has a computer with an line input.

What about your computer? Surely you did record something with it at some point? If you did, it must have some kind of audio input that you can use to record the output of your DAPs as well.

 

[richoval]

What about your computer? Surely you did record something with it at some point? If you did, it must have some kind of audio input that you can use to record the output of your DAPs as well.

nah, didn‘t record anything for a while now... those times are over unfortunately. only have a macbook pro...

 

[castleofargh]

I have no idea why anyone would recommend using white noise for volume matching DAPs, maybe @castleofargh will care to explain it? I think using a sine wave your mic can reliably pick up (so anything between 200Hz~2kHz is a good bet) is much easier to handle and just as accurate as using white noise in this case but I wouldn't use a microphone for volume matching DAPs in the first place anyways.

Probably the most accurate and complicated thing you could do is to use a multimeter if you or maybe someone you know has one, set it to measure AC voltage and measure the output voltage of your DAPs while using your headphones as a load. If you know what any of this means, you probably wouldn't ask for advice though.

If you happen to have a computer that's connected to an analog audio input like microphone inputs, or line inputs, you could just connect the output of your dap to that and record you input with some software (like Audacity for example) and match the levels using that. Just make sure you don't blow up your inputs by using too high volumes. This shouldn't be too hard to do and I think it's gotta be at least as accurate as trying to record the actual sound level of the IEMs with some microphone.

I mentioned noise(doesn't matter which) in case the app sucks with a single tone, or if the IEM happens to have low amplitude at that frequency, making it harder to get a good reference above the background noise. With noise, the SPL meter will hopefully pick up the loudest stuff, and that's that. But you're right that anything within 200Hz to 3kHz is probably going to be at a descent amplitude.

About measuring the DAP unloaded with a soundcard, not everybody will have a cable for that. Also, while chances are that you'd get the right value or at least close enough not to bother with the difference, not knowing the amp section designs or details about the IEM, I didn't want to take a chance.
Overall it might well be that I'm concerned about way too many things that won't happen ^_^.


@richoval getting reading at 1dB is certainly better than nothing, but subjectively it's more than enough for the loudness alone to make us feel like it's more than loudness difference. Now a fast check on the apple store showed non free apps. Maybe someone familiar with the apple ecosystem knows a free app to do the job?

 

[VNandor]

I mentioned noise(doesn't matter which) in case the app sucks with a single tone, or if the IEM happens to have low amplitude at that frequency, making it harder to get a good reference above the background noise. With noise, the SPL meter will hopefully pick up the loudest stuff, and that's that. But you're right that anything within 200Hz to 3kHz is probably going to be at a descent amplitude.

Maybe the reason he has a hard time matching volumes is because it's not easy to get a stable SPL reading with using noise, especially if the app's averaging is fast. This wouldn't be a problem with a sine or any other cyclic signal. A sine wave has a better crest factor than noise so it's probably for the SNR as well.

About measuring the DAP unloaded with a soundcard, not everybody will have a cable for that. Also, while chances are that you'd get the right value or at least close enough not to bother with the difference, not knowing the amp section designs or details about the IEM, I didn't want to take a chance.
Overall it might well be that I'm concerned about way too many things that won't happen ^_^.

These players have an output impedance of 1.5 and 1.6ohms according to moon audio's website which close if that's what you are worried about. I just think an "amateur" voltage measurement is going to be more precise then an acoustical measurement of similar quality.
As for the cables, I honestly expect him to have some cables lying around... 3.5 jack to 3.5 jack or 3.5 jack to RCA cables aren't special or hard to get. Although i thought he would have some audio input and I was wrong so who knows.

 

[castleofargh]

Maybe the reason he has a hard time matching volumes is because it's not easy to get a stable SPL reading with using noise, especially if the app's averaging is fast. This wouldn't be a problem with a sine or any other cyclic signal. A sine wave has a better crest factor than noise so it's probably for the SNR as well.

I don't know why I didn't think about that at all. Guess I got too comfortable using tools and apps I could fully configure to my liking. I'll go edit my first post.