Reducing overall volume range

[jcoman]

Hello, I have a RPi model B with a Polyvection PlainDAC (same chip as the Hifiberry, just a smaller form factor) driving a Sure Electronics class D (or T) 2x100W amplifier, and the overall volume level is a little louder than I would like. Normal listening range is about 15-30 on the volume knob and anything above 50 starts to get uncomfortable. I like to listen to the music really low at night, so the goal is to get more resolution down low and eliminate the upper (painful) volume levels.

I'm already supplying the amp with only 20V (range is 15-32), and the input gain on it is set to the weakest it can be, so I don't think I can change anything there. The DAC isn't the + version, so there is no hardware volume control option and I'm using Rune's software volume control. The speakers are built-in to the walls, and my guess is that they are just really sensitive.

Before I added the DACs, I was using the pi's default output (the hiss at low-ish volume levels was awful, and the intention was always to add DACs), and the overall volume level was lower than it is with the DACs (normal listening was ~40-60, and uncomfortable began around 80-90).

What would be the best way to lower the output volume? I have 4 of these setups running various zones in the house, so cheap would be good . The amps have an input impedance of ~60K from the datasheet, and I'm thinking I could just get/make a set of attenuators for the RCA (line level) cables, but a software method would be easier to implement .

I'm wondering though if a passive (resistor) attenuator might raise the average SNR because it would allow the DAC to run at a higher level for a given volume level?

Anybody have any ideas/thought?

[utschu]

Would it work by use of alsamixer which has to be started from the console?

[PeteB]

I'm wondering though if a passive (resistor) attenuator might raise the average SNR because it would allow the DAC to run at a higher level for a given volume level?

If you need the output to be at lower level, some kind of external volume control or attenuation is necessary for good results. Decent SNR and good volume control are hard to achieve, and there is nothing that can be done about it in software.

I plan to have 3~4 remote headless players, using older analog (class A/B) amplifiers which have no built-in volume control, not like a receiver, and this was one of the first things I noticed.

The signal-to-noise ratio is already not the best, but at 0db or close, you just don't notice. At lower volumes, it is degrading what would otherwise be outstanding sound. If you have high-gain amplifiers like I do, or sensitive speakers, watch out. If you have the same DAC chip as the HiFiBerry DAC+, then there are some things you can do, but your results may vary.

The normal output of the DAC is 2V rms at 0db (in my case this overdrives the input stage on some of my amps). Fortunately the chip has a setting to reduce this to 1V rms 0db, so I would try this first.

Code: Select all

[root@runeaudio ~]# amixer sset Analogue 0
Simple mixer control 'Analogue',0
  Capabilities: pvolume
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 1
  Mono:
  Front Left: Playback 0 [0%] [-6.00dB]
  Front Right: Playback 0 [0%] [-6.00dB]

Then work with the hardware volume setting, for example:

Code: Select all

[root@runeaudio ~]# amixer sset Digital 183
Simple mixer control 'Digital',0
  Capabilities: pvolume pswitch
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 207
  Mono:
  Front Left: Playback 183 [88%] [-12.00dB] [on]
  Front Right: Playback 183 [88%] [-12.00dB] [on]
[root@runeaudio ~]#

Btw, watch for blown tweeters, a year ago I fried a pair with the tap of a finger on the UI...

[jcoman]

Thanks for the thoughts, they are just confirming my suspicions. Trying to save a couple of bucks (literally ), I bought the version without the integrated volume control (The DAC instead of the DAC+), so alsamixer and any other software solutions are out. I guess my best option is a passive attenuator on the output.

The signal-to-noise ratio is already not the best, but at 0db or close, you just don't notice.

Actually, coming from using the built-in audio, the DACs sound wonderful . But you're right, at lower software volume levels, noise becomes audible

Btw, watch for blown tweeters, a year ago I fried a pair with the tap of a finger on the UI...

Thanks for that, that's part of the reason for lowering the range

[dunghnguyen]

@jcoman: you can try to plug in a keyboard into RPi, also connect its HDMI out to TV then logging in by user 'root' with password of 'rune' then simply typing the below command:

alsamixer

then you could adjust the original volume by using up/down arrow keys on the keyboard.

Hope this helps.

[jcoman]

@dunghnguyen: Thanks, but I tried that using ssh, and because i don't have the + version of the DAC (at least I think that's why) alsamixer just tells me "this device does not have volume control" or something like that. I can adjust the PCM (rpi native output) volume, but not the DAC's.

Thanks though

[dunghnguyen]

So it should have something instead, do u think so?

[jcoman]

The DAC I have doesn't connect to the pi with I2C, only I2S, so I don't think I should be able to control it from alsamixer (or the pi at all).

[PeteB]

@jcoman: I believe your DAC board may have a different dac chip, not identical to the DAC+ and the DAC+ Pro.

I read your other posts, & it looks like you are doing something similar. As for saving a few $, same here. I simply don't have the budget for 3~4 completely new sets of audio gear, so I am recycling older amps I already own and like, and same with speakers.

The scheme works great using a 25W receiver with a built in pre and volume knob. Not so much with a plain amp, especially not with 50+ wats per channel A/B amps.

A good passive volume control is not cheap, either, but: According to the DAC chip spec, the output can drive up to a 1K load (not tested yet). Therefore, building one from conventional components is not out of the question. I hope to get some time to try it, soon. Software OR hardware volume control at the chip, in this case (Pi, dac board, wallwart power supply), reduces mostly signal, not noise (tested).

In-line attenuators are your next best option, because they reduce the signal and noise proportionately, just like a passive volume control. Avoid the ones intended for cars audio...

I have tried these, and they are ok, not great, but fair to good (in my, biased, opinion):

http://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/ref=sr_1_3?s=electronics&ie=UTF8&qid=1459614951&sr=1-3&keywords=audio+attenuator