[keiron99]

I won't bore you with all the details of my set-up but I was thinking, if you're using your PC as a source, why bother with a pre-amp? Could it not be plugged directly into a power amp and the volume control on your replay software, eg iTunes be used instead of the volume control on the preamp? I'm sure the thought of this would make some purists break out in a cold sweat, but surely there's benefits in terms of fewer things in the signal path? Has anyone tried this and if so could you report back? (I can and will try this myself but it'll be a major job just getting round the back of all my equipment and finding cables long enough.)

 

[Zorander]

I have considered this a few times before (have yet to obtain a power amp that I can use for this purpose though). I agree with the thoughts of shorter signal path and simplified control scheme.

However, I am also wary of the possibility of some programs/mishaps/naughty-little-cousins-sneaking-around-your-computer that change the master volume. Imagine this worse-case scenario: music is playing through the system and the volume control is suddenly brought to max. BANG!

It may not permanently damage the speakers, but if done a few times, is almost guaranteed.

 

[Zorander]

I believe soundcard outputs are relatively high-gain, so if you were to pair one up to a power amp, you will have to set the master volume to a fairly low-level for normal volume listening. And with high-gain, a slight change in master volume results in a large change in amp output. It gets irritating when all you want is a small volume change through the speakers.

I could be wrong though since I haven't really tried this with a true power amp. Cheers!

 

[upstateguy]

Quote:

Originally Posted by keiron99 I won't bore you with all the details of my set-up but I was thinking, if you're using your PC as a source, why bother with a pre-amp? Could it not be plugged directly into a power amp and the volume control on your replay software, eg iTunes be used instead of the volume control on the preamp? I'm sure the thought of this would make some purists break out in a cold sweat, but surely there's benefits in terms of fewer things in the signal path? Has anyone tried this and if so could you report back? (I can and will try this myself but it'll be a major job just getting round the back of all my equipment and finding cables long enough.)

Hi keiron99

My understanding is that the volume control on replay software lowers your bit-rate and therefore should be left on max.

I am using the set up you are talking about (shuttle SB61G2V4 into a 110W Hitachi/Scott amp) but the problem I have is that the lowest setting on the windows volume control is still too loud for most of my headphone listening. I therefore have to lower the wave volume level as well to obtain tolerable listening levels and I'm not sure if doing that that also lowers the bit-rate like the software volume does.

Regards

USG

 

[CSMR]

Really from a PC with good quality output all you need is an attenuator to get the the max volume right and the sound card should cope fine with the few decibels attenuation you will need after that.
That's assuming that you find a way to bring up the level of quiet music, and I haven't found an easy way. (The foobar volume control only goes up to 0db.)

 

[keiron99]

Quote:

Originally Posted by upstateguy My understanding is that the volume control on replay software lowers your bit-rate and therefore should be left on max.

Thanks, but I'm reasonably sure that's not correct. I'd have thought that the software simply applies some attenuation on the level (in my case digitally, since I have an optical out from my sound card to my DAC). Bit rates don't come into it.

 

[keiron99]

Quote:

Originally Posted by CSMR Really from a PC with good quality output all you need is an attenuator to get the the max volume right and the sound card should cope fine with the few decibels attenuation you will need after that. That's assuming that you find a way to bring up the level of quiet music, and I haven't found an easy way. (The foobar volume control only goes up to 0db.)

The "0db" is, in effect, the maximum volume. In other words, no attenuation is being applied. When you turn up the volume control, you are reducing the attenuation, to the point where there is no attenuation at zero.

I suppose the question in my case specifically, since I'm using the digital output from my PC in to a DAC, is whether using the digital volume control in the software (Itunes in this case) has any negative effect on the sound quality compared to an "analogue" volume control such as in a pre amp.

 

[stefan]

I've tried using digital volume control but found it to be less intuitive than a simple knob for fine tuning. Quality difference? No idea.
There has been discussion of this over at audioasylum in the PC audio forum. One person has compared the volume pot on the Benchmark DAC1 to the volume control, via Foobar, for the digital out of a 1212m. The digital volume control was reportedly better but needed a bit of 'extra care'....

 

[Tim D]

This has been discussed before in detail. Short answer is it depends, could end up being better, worse, or not noticably different. Correctly done it can be equal or better (i.e. using 24 bit output on 16 bit normalized data gives you some headroom without loss of fidelity). Poorly done and you can be listening to 8 bit audio (FYI, it is rarely the former). So yes, it doesn't hurt bit-rate, it can hurt bit-depth.

You can think of this concept quite simply with image processing for example. Lowering brightness on a raw picture only lowers the amplitude of each pixel. Assuming we have a 8-bit grayscale in a 16 or 24-bit data format, there are brightness adjustments we can apply that will not throw away any actual contrast. But if there is a 16-bit grayscale image utilizing 16-bit of contrast and your result file is 16-bit, than any brightness change (adding or subtracting amplitude), will result in loss (meaning your whitest whites don't get any whiter or your darkest darks won't get any darker).

Analog adjustments using the same analogy, would be manipulation of lighting or optics with lens and lamps, etc. Again the end result still depends on the quality of said analog components.

Now throw in a 'noise-floor' factor into the mix with the preamp vs soundcard output, and basically the answer will still be it depends. In general, significantly attenuating your music digitally only to significantly amplify it is a bad idea. And often this is exactly what is the situation since you are using your computer to attenuate only to amplify that result.

Even ignoring sheer loss of bit-depth and thinking about just the analog realm, it can be in many instances a bad idea. You may have 24-bit digital headroom to play with, but the least significant bits might not resolve so well anyways by the time it comes out of your soundcard. So playing your 16-bit audio normalized and set towards the most significant bit (i.e. louder) is still usually better than playing that exact same 16-bit data towards the least significant bit. True there is no bit-depth loss, however I can guarantee you that your soundcard does *not* resolve full 24-bit quality such that your least significant bits are reproduced as well as your MSB's anyhow. The *true* noise floor of 24-bit audio would be -144 db or so, and no audio circuit much less soundcard I know of approaches that. That means all the bits you push towards the LSB are masked by noise floor anyhow.

Going back to the image processing example, this would be like applying a darkening on an image on an LCD monitor without truly black blacks. Maybe there isn't any digital truncation, but your analog component's performance can still mask it.

 

[30241]

Digital volume you are shaving off bits. Analog volume you are shaving off "volume?"

 

[upstateguy]

Quote:

Originally Posted by keiron99 Thanks, but I'm reasonably sure that's not correct. I'd have thought that the software simply applies some attenuation on the level (in my case digitally, since I have an optical out from my sound card to my DAC). Bit rates don't come into it.

Hi keiron

If I remember correctly, digital volume controls operate by reducing the bit depth and therefore soft sliders should be kept as high as reasonably possible, controlling the volume with the amplifier.

Regards

USG

 

[CSMR]

Quote:

Originally Posted by keiron99 The "0db" is, in effect, the maximum volume. In other words, no attenuation is being applied. When you turn up the volume control, you are reducing the attenuation, to the point where there is no attenuation at zero.

Of course 0db can be thought of as zero attenuation. It is not necessarily maximal since if you have quiet music that does not use the full 16bit range you should be able to apply negative attenuation without clipping. The point would be to keep the analog output of the sound card as high as possible. (Without this negative attenuation less attenuation must be used after the sound card, so louder music must be played back with more digital attenuation.)
Quote:

I suppose the question in my case specifically, since I'm using the digital output from my PC in to a DAC, is whether using the digital volume control in the software (Itunes in this case) has any negative effect on the sound quality compared to an "analogue" volume control such as in a pre amp.

If the DAC takes a 16bit signal this is obviously bad. If it takes a 24bit signal a preamp may or may not improve things.
In addition to bit depth and noise floors, impedance is another important issue, which I don't really understand. If the source and amplifier impedences are mismatched an active preamp will be necessary, they say.

 

[tschanrm]

Quote:

In addition to bit depth and noise floors, impedance is another important issue, which I don't really understand. If the source and amplifier impedences are mismatched an active preamp will be necessary, they say.

This isn't too much of an issue unless you are using a passive pre-amp. Most sound cards output an impedance below 2k, which is just fine for just about any amp. The generally accepted rule is 10:1; that is if your amp has a 100k input impedance, you should use a 10k or lower output from the source. Hope this helps.

 

[rickcr42]

All depends on your requirements.If you are after fast/light/cheap and have a volume control on your keyboard you have already in effect a control preamp which only needs the proper amps/speakers/headphones to get the sound out.None of these need to have a volume control.

If you are after the absolute best sound you can have then most likely you would have a breakout box,external ADC/DAC,external gain stages/controls/processing,and amps with input level sensitivity controls (not volume controls which even a headphone amp has no real need for here).

Most fall in the middle where they use the line in and line out of the sound card to external amps with built in volume controls.There is no need for any additional gain so "preamp" would be a wrong label since you will only be "amping" the headphones or speakers and will use the volume controls on the amps for that or if not available a passive attenuator/monitor switch box at most

 

[CSMR]

Quote:

Originally Posted by tschanrm This isn't too much of an issue unless you are using a passive pre-amp. Most sound cards output an impedance below 2k, which is just fine for just about any amp. The generally accepted rule is 10:1; that is if your amp has a 100k input impedance, you should use a 10k or lower output from the source. Hope this helps.

Does a passive preamp raise source impedence as compared with a direct connection?