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Does the Pure Direct Button Really Enhance Sound Quality?

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#1
What does bypassing tone and loudness controls do exactly to enhance an amplifier's sound quality?
Can anyone actually hear the difference? (I can't)
If anyone can hear the difference, what does this difference consist of?
 
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#2
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#3
The way I see it, if you use analog inputs with Pure Direct, then it bypasses built-in DAC, DSP and all other gimmicks. In this mode it's pure amplifier without any sound processing.
 

pozz

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#4
The way I see it, if you use analog inputs with Pure Direct, then it bypasses built-in DAC, DSP and all other gimmicks. In this mode it's pure amplifier without any sound processing.
I would just add that, although that's the basic idea, you can't really know this without studying the circuit diagrams and then measuring.

Amir's AVR measurements generally show better performance using pure direct mode. Check out the master review thread for a few examples.
 

pozz

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#5
What does bypassing tone and loudness controls do exactly to enhance an amplifier's sound quality?
Can anyone actually hear the difference? (I can't)
If anyone can hear the difference, what does this difference consist of?
I meant to add that the differences as they've been measured are usually not significant.
 

L5730

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#6
Pure Direct on an all analogue integrated amplifier is only going to bypass the tone controls, loudness and maybe balance control.
It should, I guess, slightly reduce any noise imparted through that circuit by having a pure direct path.

In A/V amplifiers, the function can turn off a lot of DSP processing. The more expensive models tend to fully turn off all the DSP, so nothing comes out of the centre channel and maybe not the subwoofer channel.

In my experience with an older consumer Yamaha integrated 2 channel unit, it did make a really tiny difference. On the newer model, it seems to make no audible difference to me. Sighted tests, so my findings aren't conclusive. I don't know about A/V stuff, haven't tried with it, only read a lot about them when thinking of getting one instead of 2 channel.
 

North_Sky

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#7
There is so much happening in AV receivers nowadays...Ethernet, Appple TV, Alexa, Bluetooth, DSP, ADC, DAC, Dolby Vision passthrough, eARC, HEOX, IMAX mode, 13 and 15 channels of manipulation (bass massaging) and amplification, Tidal, Roon, MQA, HDCD, DSD, ... it's not like yesterday's stereo AM/FM receivers with a Tone Bypass button. An AV receiver today is like the space shuffle, like a Tesla electric car, like Microsoft control center, like Amazon worldwide infrastructure, like Donald Trump organization, ...

Pure Direct audio mode doesn't do anything magic to my ears that Direct and Stereo cannot either. It sounds all the same to my set of ears. Trying to listen for differences/variations give me a bad headache after hours of extensive attentive listening, after days, weeks, months, years, decades, centuries, milleniums, different galaxies, other multiverses, 3 and 4D rainbows, ...

It might sligthly measure better on paper graphs but not in my real life listening music and film soundtracks experience. IMHO, YMMV, ALLTHATPLUTOJAZZ.
 

L5730

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#8
Without derailing, I'd love a pure direct button to cut through a politicians BS! Press a button on the TV and the politician's gain drops and has a voice over by someone saying "blah, blah, white lie, blah, blah, get country into more debt, blah, blah ..." :)

Jeepers! I haven't looked at modern A/V amps. An appliance that has got over complicated with a possibly clunky UI. No thanks, I'll use a PC and know that's it's complicated. USB DAC > Stereo analogue amplifier, simpler life :)
 

Kal Rubinson

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#9
The more expensive models tend to fully turn off all the DSP, so nothing comes out of the centre channel and maybe not the subwoofer channel.
Why? If you feed a discrete center and/or sub channel signal in, it should come out.
 

L5730

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#10
Why? If you feed a discrete center and/or sub channel signal in, it should come out.
Sorry, for clarification, I meant, feeding 2 channel stereo and the DSP 'making up' something for the center channel.
Bob Clearmountain mentions it when doing the 5.1 of Roxy Music's Avalon album...

https://www.soundonsound.com/people/recording-remixing-roxy-musics-avalon

"The manufacturers of consumer gear should put a really obvious button on their systems saying Music," says Bob Clearmountain. "Most of the home systems are designed for movies, and have extra DSP built in to create some sort of theatre ambient effect, and they have automatic level controls. Those are the last things you'd ever want for listening to music. A lot of systems default to having them switched on, which means that if you play music, you get one big bass drum or tom-tom, and it kicks the level right back. It's usually buried 10 menus deep. But how are people supposed to know that? It was tough for me to find on my Sony. You get the general public out there and they're lucky if they get the speakers in phase. How are they going to know to do that?

"You really don't have much control over how things are played back. There's this whole bass management issue, which I still don't quite understand. I just know that on my Sony receiver at home, I noticed that if I didn't put anything in the LFE channel, the system made up its own LFE, and it sounded terrible. It would just take some kind of sum of the other channels and create a subwoofer channel. But when I did use the LFE channel it was just what I put in, and it sounded much better. A lot of people told me 'For music, don't put anything in the LFE channel, that's only for movies.' But then I started doing it and when I played it on my system it just sounded right, when I had control over it. But depending on how you have your system set up, that could be wrong. I just put stuff in the LFE channel and let the mastering guy worry about it!"
I'm sure I read something else about this album, but this was easy to find.
 

restorer-john

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#11
What does bypassing tone and loudness controls do exactly to enhance an amplifier's sound quality?
I've seen every type of tone defeat, direct, pure direct, power amp direct etc known to man over the years. In AVRs it gets even more hairy and is hardly transparent in its operation- one needs to study the schematic.

The original "tone defeat" functions took the tone stage out of the path. The original "direct" functions took the tape outs, the filters and the tone stages out of the path. The "line/source direct" often took a high level signal to a volume pot and straight to the power amp.

Not all bypass functions improve responses, but most make an attempt to remove active and passive circuitry that is not needed. Many are deliberately set to give a slightly higher perceived level when bypass/direct is engaged to make you think it is "better".

Here's an example. Yellow and purple are offset L/R through the tone stages. The top plot is "defeat". Notice it is worse with roll-off at both frequency extremes.(bottom plot is low and high filters engaged) This particular amplifier has a flatter response with the tone/filter circuitry engaged...
1152dc.JPG
 

bobbooo

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#12
I did a quick very unscientific test comparing the noise level of my Denon X2400H AVR using the Stereo Auto, Direct, and Pure Direct modes (without Audyssey room EQ set up). Using a sound level app with my phone's mic an inch from the tweeter, the noise level was 2dB higher using Auto mode than the 'direct' modes (both the same as far as I could tell), with the AVR's volume set to max (streaming HEOS source). So it does look like the direct modes make a difference. Whether this difference would be audible at normal listening levels and distances is debatable though. This needs more investigation really, with real measurements or blind ABX tests, rather than anecdotal sighed impressions that are highly susceptible to expectation bias.
 
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#13
On my A/V receiver, "Pure Direct" makes a HUGE difference.

As L5730 notes, it turns off all EQ (including Audessey) and phase control, and disables bass management via the .1 channel. So my system sounds COMPLETELY different.

Now, if I weren't using EQ / Audessey and bass management at all, perhaps there would be little effect ... but why would you use a receiver without using its most useful features? ;)
 
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#14
As with all audio systems, the entire audio chain, speakers, room, source, recording quality, play a part in “audible difference”.

In my former setups I could not tell much of an audible difference with direct/bypass engaged. With my current system I was using an Anthem avm 60. I wasted so much time running room correction trying to make it sound better. One day I randomly pushed the direct button the avm60, while playing a cd from my oppo 205. The sound was light years better. I couldn’t use my subs with direct engaged so I auditioned some 2 channel preamps. I tried a Macintosh C47 and the Moon 390. Both were remarkably better than the AVm 60. I sold the Anthem and bought the moon 390.

I knew the oppo 205 was an excellent dac thanks to Amir’s test results, so it wasn’t hard to compare all 3 preamps using the oppo as reference.

So, does direct make an “audible difference?”
Yes and maybe
 

restorer-john

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#15
Here's some quick tests of a couple of vintage preamplifiers at 1V in 1V out comparing direct off with direct on. Same ARTA FFT settings as @pma (except he uses exponential averaging) so they can be compared. As the direct switches only affect the front end, it makes sense to test standalone preamplifiers with that function as noise from amplifier stages won't swamp the readings as they would in an integrated amplifier.

Yamaha CX-600.
Direct off first:
yamaha cx-600 left channel direct off.png

yamaha cx-600 right channel direct off.png


Direct on:
yamaha cx-600 left channel direct on.png

yamaha cx-600 right channel direct on.png


And a Sony TAE-77esD preamplifier. Direct off first:
Sony TAE-77esD leftt channel direct off.png

Sony TAE-77esD right channel direct off.png


Direct on:
Sony TAE-77esD left channel direct on.png

Sony TAE-77esD right channel direct on.png


I think you get the picture. It depends. The Yamaha it made a big difference (in the right channel), the Sony not so much, but the Sony has some junk clearly from the remocon/micro or from the onboard D/A converter (unused) spewing a little rubbish at the top end. I'll compare the non-D/A equipped TAE-77es to see if it's from the DAC inside.

The limit with both these is the soundcard, here's the loopback (analogue)- it's in my LAB PC. (an old M-Audio AP 24/96) The preamps are essentially adding nothing of note except some LF noise and in the case of the Sony, a bit of HF noise.

Img.jpg


I'll run the same tests on a different card inside that machine (there's two PCI cards in it), the old M-Audio AP 24/192, as it has a better performance and balanced inputs. Note, the dBV levels (not absolute, comparative) vary a little as the main volume pot was used to balance direct with bypass and still keep the input level the same.
 
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restorer-john

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#16
Here for comparison is a Sony TAE-77es which is identical to the TAE-77esD except without the onboard D/A converter and a few extra inputs.

Direct off first:
Sony TAE-77es left channel direct off.png


Sony TAE-77es right channel direct off.png


Direct on:
Sony TAE-77es left channel direct.png


Sony TAE-77es right channel direct.png


Improvement in the 50Hz and its harmonics, that's all. Time for a new soundcard as the preamp's distortion is negligible.
 
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