PC Audio questions

The place to sound off on all things related to audio, from sound cards to speakers.

Moderator: Captain Ned

Re: PC Audio questions

Postposted on Thu Mar 27, 2014 8:23 pm

superjawes wrote:We aren't confusing definitions (I put "perfect" in quotations for a reason). As JBI pointed out, op amps use negative feedback, and as long as you stay within the voltage rails and below the maximum slew rate, the internal components are basically irrelevant to the voltage response of the output. This is what I mean when I say they are designed to be "perfect." If the frequency response is anything but flat (in the audio range), then the design engineer has failed.


Well, this is getting beyond my knowledge, but wouldn't differences in slew rate, for instance, possibly effect things like how quickly the circuit responds to changes in signal amplitude (i.e., voltage demand)? So that one op amp with a slower slew rate might perhaps have a more tube like (warmer) sound through introduction of more transient distortion? This is an over-simplification, but what I'm getting at, is, wouldn't varying these basic op amp parameters by applying different input/output circuitry design potentially have a subtle impact on the sound?
cynan
Gerbil Elite
Gold subscriber
 
 
Posts: 837
Joined: Thu Feb 05, 2004 2:30 pm

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 2:50 am

cynan wrote:Well, this is getting beyond my knowledge, but wouldn't differences in slew rate, for instance, possibly effect things like how quickly the circuit responds to changes in signal amplitude (i.e., voltage demand)? So that one op amp with a slower slew rate might perhaps have a more tube like (warmer) sound through introduction of more transient distortion? This is an over-simplification, but what I'm getting at, is, wouldn't varying these basic op amp parameters by applying different input/output circuitry design potentially have a subtle impact on the sound?

Slew rate does affect how quickly the circuit responds, but this is a matter of "is it fast enough for the given application?" The upper range of human hearing is 20 KHz. The slew rate of an op amp is typically measured in volts per microsecond. Do the conversion to frequency, that means that you won't bump into this limit until you're in the Megahertz range, much higher than any human can hear. That isn't a "subtle" impact on the sound, it's a negligible one.

And this is exactly why people like op amps for voltage amplifiers. If you operate within the basic parameters, you can essentially eliminate the distorting effects that occur when using discrete designs. This is, of course, very boring compared to discrete designs, which is why we still have tube amplifiers on the market when we can develop transistors that are measured in nanometers.

And it should also be mentioned that op amps aren't necessarily good current sources, so delivering enough power to drive speakers and/or headphones can be a problem (so this is another advantage of discrete amplifier designs).
Damage wrote:Don't try to game the requirements by posting everywhere, guys, or I'll nuke you from space.

-Probably the best Damage quote ever.
superjawes
Graphmaster Gerbil
Gold subscriber
 
 
Posts: 1143
Joined: Thu May 28, 2009 9:49 am

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 11:55 am

superjawes wrote:Slew rate does affect how quickly the circuit responds, but this is a matter of "is it fast enough for the given application?" The upper range of human hearing is 20 KHz. The slew rate of an op amp is typically measured in volts per microsecond. Do the conversion to frequency, that means that you won't bump into this limit until you're in the Megahertz range, much higher than any human can hear. That isn't a "subtle" impact on the sound, it's a negligible one.

And this is exactly why people like op amps for voltage amplifiers. If you operate within the basic parameters, you can essentially eliminate the distorting effects that occur when using discrete designs. This is, of course, very boring compared to discrete designs, which is why we still have tube amplifiers on the market when we can develop transistors that are measured in nanometers.

And it should also be mentioned that op amps aren't necessarily good current sources, so delivering enough power to drive speakers and/or headphones can be a problem (so this is another advantage of discrete amplifier designs).


Well, in my above post, I suppose I didn't mean "voltage demand" but overall "power demand". Maybe it's the characteristic of op amps you describe of not being as flexible in supplying demanded current as they are with voltage that introduces this distortion. This is certainly speculation on my part, but I still think that the reason why some people prefer (or at least claim to) like warmer vs more clinical sound has to do with the introduction of distortion (purposeful) - which is likely to be more prevalent at different frequency ranges due to current demands,etc.

After all, isn't that what is going on when people "roll" (ie, switch) vacuum tubes in pre-amplification/amplification stages with tube amps? Different tubes impart different distortion characteristics...

Interestingly, going back the guy that designed those op amps I linked to previously, in his mid and higher end DACs, he claims that a non-feedback designs sound favorable to most of his customers and so has switched to these designs over the last few years. He fully acknowledged that these designs, as measured, show more distortion. But says that feedback from internal auditioning, and from customers suggests that people prefer the result. Basically, over the years, he's played around with a bunch of different circuit designs, and while measuring their performance analytically, claims that, in the end, he just sticks with what sounds best, regardless of whether they don't measure as well. Quite a different perspective from what you'd find in most electrical engineering applications (and I could see how many engineers would write this off as BS at face value). The main method by which performance is upheld while using a non-feedback design is through the use of something called "current conveyor technology" which is apparently a discrete means of increasing signal gain by converting a current signal directly to voltage without a traditional op amp config in the pre-amplification stage...you can read a bit about it here if interested)

(And yes, we are talking about pre-amplification analog output stages. Obviously the main amplification stages are discrete.)
cynan
Gerbil Elite
Gold subscriber
 
 
Posts: 837
Joined: Thu Feb 05, 2004 2:30 pm

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 12:39 pm

Yes, but tubes are a very different animal. Tube circuits typically use less (or no) negative feedback, so any non-linearities in the transfer function of the tube affect the shape of the waveform, and will color the sound. The negative feedback used in op amp circuits eliminates non-linearities unless you're exceeding the op amp's specifications in some way. Equating the swapping of op amps in a DAC circuit with swapping of tubes in a tube amp is an apples-to-oranges comparison.

As noted, some op amps are not particularly good at sourcing/sinking current. This can result in reduced output voltage swing (hard clipping), and (for op amps which use push-pull output configuration) crossover distortion when driving low impedance loads. So yes the specs of the op amp do matter to a point; but as long as you've got one with sufficient output drive capability for the application, it should not "color" the signal because the output is a faithful linear scaling of the input. Furthermore, unlike subtle non-linearities, hard clipping and crossover distortion tend to be rather obvious; if you've got 'em, the effects will not be subtle!

Regarding the non-feedback designs... it all comes down to personal preference. If it sounds better to someone, then yeah it is worthwhile to that person. But at the end of the day, you have a LESS faithful reproduction of what the recording engineer intended.
(this space intentionally left blank)
just brew it!
Administrator
Gold subscriber
 
 
Posts: 37974
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 12:44 pm

just brew it! wrote:Furthermore, unlike subtle non-linearities, hard clipping and crossover distortion tend to be rather obvious; if you've got 'em, the effects will not be subtle!

Aided by the fact that IC distortion is odd-order whereas tube distortion is even-order, and to human ears odd-order sounds bad and even-order isn't even noticed until well into the single digits and sounds "good" when it is noticed. Why else do guitarists still flock to amps driven by 6L6 or EL34 tubes (the KT series would be overkill for a guitar amp, though I'm sure it's been done)?
Life is hard; but it's harder if you're stupid. Big Al.
Captain Ned
Global Moderator
Gold subscriber
 
 
Posts: 20552
Joined: Wed Jan 16, 2002 7:00 pm
Location: Vermont, USA

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 12:50 pm

This is a bit of an over-simplification/over-generalization, but odd-order harmonic distortion tends to sound harsh and grating, whereas even-order tends to be perceived as warm and full.
(this space intentionally left blank)
just brew it!
Administrator
Gold subscriber
 
 
Posts: 37974
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 1:41 pm

just brew it! wrote:Yes, but tubes are a very different animal. Tube circuits typically use less (or no) negative feedback, so any non-linearities in the transfer function of the tube affect the shape of the waveform, and will color the sound. The negative feedback used in op amp circuits eliminates non-linearities unless you're exceeding the op amp's specifications in some way. Equating the swapping of op amps in a DAC circuit with swapping of tubes in a tube amp is an apples-to-oranges comparison.

As noted, some op amps are not particularly good at sourcing/sinking current. This can result in reduced output voltage swing (hard clipping), and (for op amps which use push-pull output configuration) crossover distortion when driving low impedance loads. So yes the specs of the op amp do matter to a point; but as long as you've got one with sufficient output drive capability for the application, it should not "color" the signal because the output is a faithful linear scaling of the input. Furthermore, unlike subtle non-linearities, hard clipping and crossover distortion tend to be rather obvious; if you've got 'em, the effects will not be subtle!
Linearity. That's basically what it all comes down to. Op amps (with negative feedback) are very good at being linear (again, provided you stay within voltage rails and slew rates). Power is another beast. JBI noted that you can get hard clipping if you hit current limits, but it can also translate into weak sound output. Frequency response, however, is very, very flat thanks to the linearity of op amps.

just brew it! wrote:Regarding the non-feedback designs... it all comes down to personal preference. If it sounds better to someone, then yeah it is worthwhile to that person. But at the end of the day, you have a LESS faithful reproduction of what the recording engineer intended.
If you want some interesting reading on the subject of personal preference, Harman International is doing research on what constitutes a "good" sound for headphones. I've been reading this through Inner Fidelity (most recent writeup linked).

It's interesting because there is already a pair of headphones (NAD VISO HP50) that was designed based on this research, but they also found that the right frequency balance for "a good speaker in a good room" isn't necessarily a good response for "head-mounted speakers".
Damage wrote:Don't try to game the requirements by posting everywhere, guys, or I'll nuke you from space.

-Probably the best Damage quote ever.
superjawes
Graphmaster Gerbil
Gold subscriber
 
 
Posts: 1143
Joined: Thu May 28, 2009 9:49 am

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 4:12 pm

superjawes wrote:It's interesting because there is already a pair of headphones (NAD VISO HP50) that was designed based on this research, but they also found that the right frequency balance for "a good speaker in a good room" isn't necessarily a good response for "head-mounted speakers".

Yes, that *is* interesting. I guess I can sort of see how it could come about though; the coupling of the drivers to your ears is very different since they are aimed more or less directly down your ear canal, and are isolated from each other. So the way the sound interacts with your pinnae (outer part of your ear) is going to be different, and you also won't get any of the interference/phasing effects that happen when the signals from left and right speakers arrive at your ears (potentially reinforcing or partially canceling each other out at certain frequencies).

Also, since everyone's pinnae are shaped slightly differently (kind of like fingerprints), the effects probably vary somewhat from individual to individual. This is one of the reasons headphone-based positional audio is so difficult to get "right"... but that's another discussion!
(this space intentionally left blank)
just brew it!
Administrator
Gold subscriber
 
 
Posts: 37974
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 5:31 pm

One last stab at the op amp thing (and then I bow to the wisdom of those more knowledgeable :D ).

In Geoff's recent review of the Gigabyte motherboard with the replaceable op amps, he discovered that the LT1358had non-flat frequency response at the extremes of the frequency range (but well within what most would consider audible range). At the upper end, it almost looks like someone purposefully applied a low pass filter (that some might implement to make the treble less "fatiguing" to use a description). So if all op amps are flat, given that they have similar design specs, then what's up with the LT1358? Is this just measurement error? And if variations can be implemented in this relatively uncomplicated output stage design, simply by switching pedestrian, SMD op amps, compared to what is used in some higher end sources (ie, DACs), then? Is the LS1358 being driven out of spec? Not that you could tell from the subjective auditioning...

As for the tubes vs op amp stages, perhaps they are an apples-oranges. But not that dissimilar in application if we're talking about a tube stage used as a pre preamp buffer (ie, placed between the DAC and the input to the preamp/amplifier), insofar as how they might be used to modify a source analog signal. Op amps are also used in/as output stage buffers (edit: though perhaps more to lower impedance than anything else).

superjawes wrote:If you want some interesting reading on the subject of personal preference, Harman International is doing research on what constitutes a "good" sound for headphones. I've been reading this through Inner Fidelity (most recent writeup linked).


I'm kind of surprised to see the HD-600 bass being negatively compensated below 40-50Hz so strongly, even more so than the Denon A5000 - the latter which I thought had much more bass response.
cynan
Gerbil Elite
Gold subscriber
 
 
Posts: 837
Joined: Thu Feb 05, 2004 2:30 pm

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 6:29 pm

just brew it! wrote:Yes, but tubes are a very different animal.

Yes. What we really need is more vacuum tubes and wood knobs for PC audio. It makes such a difference with $50 computer speakers, and we surely won't discuss matching speakers to go with said dacs, because everyone already knows what speakers to use, and they're easily available and affordable. Positional audio, and additional features that actually enhance sound in games are completely pointless, and don't matter to PC users at all. Games like Titanfall are what every PC game should aspire to be, since uncompressed audio is the only way to truly enjoy audio through fancy dacs. This is the state of PC audio, and why we are where we are today.

I have a regular soundcard, and I have a regular 5.1 and headphone set. It's good enough for what I use it for, and I'm not a music fan. Music needs to move beyond cds, for any of this other hardware to be even vaguely useful. Another problem is finding what music is actually worth listening to. I don't like pop trash or boring soft rock type music, and I have to somewhat like the artist who's playing it. Because of that, I'd rather listen to game soundtracks and even midi more than modern bands.

I'd like to see pics of people's rigs in these audiophile e-peen threads. For the most part, I think the majority of this stuff is blowhard circle-jerking nonsense, and it probably is. Audiophile equipment is not a universal answer to PC audio, as your hardware needs greatly depend on your usage scenario and personal preference, which differ for everyone. Games on the other hand, always benefit from improved positional audio, as hearing your opponents is more important than whatever dac you're using. Not that I think dacs are useless, but a lot of it depends on external variables that are rarely discussed in conjunction with the hardware.
l33t-g4m3r
Gerbil Jedi
Silver subscriber
 
 
Posts: 1995
Joined: Mon Dec 29, 2003 2:54 am

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 6:46 pm

l33t-g4m3r wrote:I have a regular soundcard, and I have a regular 5.1 and headphone set. It's good enough for what I use it for, and I'm not a music fan.

I use onboard unless I'm recording from an external analog source.

l33t-g4m3r wrote:Music needs to move beyond cds, for any of this other hardware to be even vaguely useful.

That's not even necessary. CDs mastered with proper noise-shaped dithering are already capable of fidelity beyond what 99.9% of people can hear. 24-bit resolution and higher sampling rates are useful in a studio context because they minimize the cumulative effects of quantization error during mixing and mastering, but as a distribution medium for finished product "CD quality" is already good enough.

I would be thrilled to death if online music downloads would switch to FLAC, even if they stay at 16-bit 44.1 kHz.

l33t-g4m3r wrote:Another problem is finding what music is actually worth listening to. I don't like pop trash or boring soft rock type music, and I have to somewhat like the artist who's playing it. Because of that, I'd rather listen to game soundtracks and even midi more than modern bands.

You do realize there's this newfangled thing called "The Internet" where obscure bands and small independent labels can sell their music direct to the public, yes? Just checking.

l33t-g4m3r wrote:I'd like to see pics of people's rigs in these audiophile e-peen threads. For the most part, I think the majority of this stuff is blowhard circle-jerking nonsense, and it probably is. Audiophile equipment is not a universal answer to PC audio, as your hardware needs greatly depend on your usage scenario and personal preference, which differ for everyone. Games on the other hand, always benefit from improved positional audio, as hearing your opponents is more important than whatever dac you're using. Not that I think dacs are useless, but a lot of it depends on external variables that are rarely discussed in conjunction with the hardware.

As noted above, I generally use onboard unless I'm recording something. Which probably completely wrecks my credibility with the "audiophile" crowd. :lol:
(this space intentionally left blank)
just brew it!
Administrator
Gold subscriber
 
 
Posts: 37974
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: PC Audio questions

Postposted on Fri Mar 28, 2014 9:46 pm

I just brought my system back up after far too long. The HD Intel stuff my mobo puts out is not nice stuff. The little Muse DAC produces a whole other level of quality.

if you listen to your onboard audio, the little Muse is only $55.
Fuji X-E1 Leica Elmar 135 4 XF60mm 2.4 Macro | Zeiss FE 35mm 2.8
http://carnagepro.com
"Everything ... they eat everything, and fear is their bacon bits."
PenGun
Gerbil Elite
 
Posts: 791
Joined: Fri Jun 18, 2004 1:48 pm
Location: BC Canada

Re: PC Audio questions

Postposted on Sat Mar 29, 2014 2:32 pm

l33t-g4m3r wrote:What we really need is more vacuum tubes and wood knobs for PC audio...


Well, some people can't tell (or don't care about) the difference between 480p and HD, or 720p and 1080p... Or playing games at 30 fps vs 60 fps, or with refresh rates higher than 60 Hz, or about having a gpu that enables them to turn up the image quality settings, etc. To each their own. Fact of the matter is, most onboard audio (I have auditioned) sounds pretty inferior to even moderate add on internal (sound cards)/external DACs. I use onbaord analog for the mic input, the odd time I use one when playing a game or for voice chat at my computer. Yes, I could invest in better USB mic, but I just don't care/need one for what I use it for.

You finish your post declaring "hardware needs greatly depend on your usage scenario and personal preference" but seem to start off basically saying that everyone has $50 speakers and that positional audio in games is the only thing that matters. (But to be honest, I'm sure what point you are making in the opening paragraph, or whether what you say about Titanfall is sarcasm...).

If you'd taken the time to read the last few posts instead of just picking a quote at random, you'd have seen that no one was recommending spending $100s on computer audio, or that everyone should be interested in tubes or other enthusiast, non-mainstream equipment. Audiophile e-peen thread? I think the most expensive product actually recommended was a <$250 external DAC/headphone amp combo... How many more times expensive was this than your sound card? (And wait, you have a sound card? :o Fancy yourself an audiophile or something? :P )

And just try and pry my collection of prized wooden knobs out of my cold, dead hands! :P (though my desktop headphone amp doesn't use a potentiometer)
cynan
Gerbil Elite
Gold subscriber
 
 
Posts: 837
Joined: Thu Feb 05, 2004 2:30 pm

Re: PC Audio questions

Postposted on Sat Mar 29, 2014 4:58 pm

l33t-g4m3r wrote:
just brew it! wrote:Yes, but tubes are a very different animal.

Yes. What we really need is more vacuum tubes and wood knobs for PC audio. It makes such a difference with $50 computer speakers, and we surely won't discuss matching speakers to go with said dacs, because everyone already knows what speakers to use, and they're easily available and affordable. Positional audio, and additional features that actually enhance sound in games are completely pointless, and don't matter to PC users at all. Games like Titanfall are what every PC game should aspire to be, since uncompressed audio is the only way to truly enjoy audio through fancy dacs. This is the state of PC audio, and why we are where we are today.

I have a regular soundcard, and I have a regular 5.1 and headphone set. It's good enough for what I use it for, and I'm not a music fan. Music needs to move beyond cds, for any of this other hardware to be even vaguely useful. Another problem is finding what music is actually worth listening to. I don't like pop trash or boring soft rock type music, and I have to somewhat like the artist who's playing it. Because of that, I'd rather listen to game soundtracks and even midi more than modern bands.

I'd like to see pics of people's rigs in these audiophile e-peen threads. For the most part, I think the majority of this stuff is blowhard circle-jerking nonsense, and it probably is. Audiophile equipment is not a universal answer to PC audio, as your hardware needs greatly depend on your usage scenario and personal preference, which differ for everyone. Games on the other hand, always benefit from improved positional audio, as hearing your opponents is more important than whatever dac you're using. Not that I think dacs are useless, but a lot of it depends on external variables that are rarely discussed in conjunction with the hardware.


Oh well.I run an all tube, well almost, system and it's a very fine system. I have heard better, but only at ten times my price, in a Audiophile HiFi store.

It deals with digital music very well and as a game sound system is kinda awesome.

Thought I'd see if you were still hungry. ;)
Fuji X-E1 Leica Elmar 135 4 XF60mm 2.4 Macro | Zeiss FE 35mm 2.8
http://carnagepro.com
"Everything ... they eat everything, and fear is their bacon bits."
PenGun
Gerbil Elite
 
Posts: 791
Joined: Fri Jun 18, 2004 1:48 pm
Location: BC Canada

Re: PC Audio questions

Postposted on Mon Jul 21, 2014 10:04 am

Captain Ned wrote:Why else do guitarists still flock to amps driven by 6L6 or EL34 tubes (the KT series would be overkill for a guitar amp, though I'm sure it's been done)?

Ned, Ned, Ned. I'm disappointed.

You of all people lived through the crazy years of guitar, so how can you even conceive that anything is "too overkill" to be used in a guitar, amp, pedal, or speaker? Have you forgotten about the holy rule of going to 11? I mean, I'm fairly sure that someone out there has thought of using KT tubes in guitar amps before.

According to lots of people, they're pretty good for power amp sections.

(I'm kidding, please point that potato cannon away from me.) :lol:
There is a fixed amount of intelligence on the planet, and the population keeps growing :(
morphine
Grand Admiral Gerbil
Silver subscriber
 
 
Posts: 10067
Joined: Fri Dec 27, 2002 8:51 pm
Location: Portugal (that's next to Spain)

Re: PC Audio questions

Postposted on Mon Jul 21, 2014 7:47 pm

The LT1358 datasheet shows some fairly interesting stuff, if anyone cares: http://cds.linear.com/docs/en/datasheet/135859fb.pdf

The output impedance vs. frequency graph on page 7 and the gain and phase vs. frequency graph on page 8 don't at all match the theoretical description of op-amp behavior eariler in the thread (they clearly show the drop-off past 10 KHz). As for why, I have no clue.
deepblueq
Gerbil
 
Posts: 36
Joined: Sat May 17, 2014 9:32 pm
Location: the middle of nowhere

Re: PC Audio questions

Postposted on Mon Jul 21, 2014 9:02 pm

deepblueq wrote:The LT1358 datasheet shows some fairly interesting stuff, if anyone cares: http://cds.linear.com/docs/en/datasheet/135859fb.pdf

The output impedance vs. frequency graph on page 7 and the gain and phase vs. frequency graph on page 8 don't at all match the theoretical description of op-amp behavior eariler in the thread (they clearly show the drop-off past 10 KHz). As for why, I have no clue.

It is because the frequency response graph is showing the "open loop" response, where the amp is operated with no negative feedback. Normally an op amp is used with substantial negative feedback, which "programs" the effective gain to a predetermined value. This also has the effect of flattening out the frequency response.

For the impedance graph, things stay below 1 ohm out to 20 kHz, provided the voltage gain is kept below 10.

Take a look at the last two graphs on page 7. In this limiting case the amp has been wired for 100% negative feedback (referred to as "unity gain"). In this configuration the amp provides substantial current (and hence power) gain, but no voltage gain. At unity gain, the frequency response is ruler-flat out past 10 MHz.
(this space intentionally left blank)
just brew it!
Administrator
Gold subscriber
 
 
Posts: 37974
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: PC Audio questions

Postposted on Wed Jul 23, 2014 11:23 am

Ah, right. :oops:

So, investigating more closely, nothing in the datasheets for any of those makes the measured drop make sense, particularly since all the other parts so exactly match each other in performance. (I'm not an EE, as already shown.) I wonder if the LT1358 that came with TR's G1.Sniper 5 was a counterfeit, or compromised in some other way?
deepblueq
Gerbil
 
Posts: 36
Joined: Sat May 17, 2014 9:32 pm
Location: the middle of nowhere

Previous

Return to Echo Vale

Who is online

Users browsing this forum: No registered users and 3 guests