THD and DAC specs - how important? (1 Viewer)

[ThomasL]

When comparing receivers, how much importance do people give to THD ratings. I noticed that, for example, Pioneer's D811S is rated as follows:

Continuous average power output of 100 watts*

per channel, min., at 8 ohms, from 20 Hz to

20,000 Hz with no more than 0.2 %** total

harmonic distortion (front).

while the Marantz SR5200 is rated as follows:

Continuous Power Output (8 ohms / 20 Hz - 20 kHz)

Front.................... 90 W

Center................... 90 W

Surround................. 90 W

THD Front (20 Hz - 20 kHz) ............ 8 ohms 0.05 %

and finally the Onkyo 600 is rated as follows:

Continuous average power output (FTC)

All channels: 80 W per channel min. RMS at 8 ohms ., 2

channels driven from 20 Hz to 20

kHz with no more than 0.08% total

harmonic distortion.

It seems all 3 are only telling us what the THD is with 2 channels driven, but the Pioneer seems to have a higher THD. If one listens at lower volumes and never comes close to pushing the limits of the receiver, does this rating matter?

Also, what overall difference does different rated DACs have? For example, the new Onkyo 600 says that it has a state of the art 192Khz/24 bit DAC for PCM sources yet

Marantz SR5200 says it has a 96Khz/24 bit DAC. Is Onkyo's going to be much better?

How much do people weigh the various differences in these specs when choosing a receiver?

thanks,

--tom

 

[Darin J]

Being new to the home theater scene, I hope someone who understands how power ratings translate into audible quality replies to this topic.
I've been considering the Pioneer VSX-811S as a less costly option to the Onkyo SR-600 as well. My only concern has been whether I will notice a significant sound difference at normal listening levels.
I saw a review of the Pioneer D850S along with the Denon 1802 and a Sony a few months ago and the Pioneer's performance was considered very good. It seemed like Pioneer was very conservative on their power ratings. I don't know if the D811S has comparable internals but hopefully it does.
Surprisingly, none of the stores in my area carry the Pioneer D811S so I can't get a listen. However, I'm very eager to make a purchase since I don't even have Digital Dolby in my current receiver. The Onkyo is a safe bet but its $150 more than the Pioneer based on the best prices I've found on the internet.
Adding to the budget reciever mix, Kenwood now has a VR-6060 with comparable features to the two above and the following power ratings:
- Stereo Power: 100 Watts per Channel (Left/Right, 20Hz - 20kHz, 0.09% THD, 8 ohms)
- Surround Power (Center): 100 Watts (20Hz - 20kHz, 0.09% THD, 8 ohms)
- Surround Power (Left/Right): 100 Watts + 100 Watts (20Hz - 20kHz, 0.09% THD, 8 ohms)
- Surround Power (LSurround/RSurround): 100 Watts + 100 Watts (20Hz - 20kHz, 0.7% THD, 8 ohms)
- Surround Power (Selectable--Subwoofer/Surround Back): 100 Watts (20Hz - 20kHz, 0.09% THD, 8 ohms)
I'd be interested in comments on whether the Kenwood would be considered better than the Pioneer. I haven't been able to find any discount prices on the Kenwood yet but expect it to come close to the Pioneer in price.
It seems everyone is finally coming out with their Prologic II and 6.1 systems. I could wait for new products and lower prices forever but I want to start enjoying better sound sooner rather than later.

 

[Saurav]

IMO, the difference between 80, 90 and 100 watts will be negligible, or at least, not significant enough to be a big factor in the buying decision. I'm not really sure about how much difference in THD will be audible, 0.2% and 0.05% does seem like a fair amount. Of course, I'm running tube amps with 1% THD and I think they sound better than the solid state amps I had before, so if I were making this decision, I wouldn't put much importance to THD numbers either, I'd prefer to go listen to the 3 receivers, with the same (or similar) source/speakers/room if possible. I believe most other people on here give more importance to THD than I do

 

[keir]

According to the FAQ at Yamaha's page, we can't hear any THD under 2%. I can't tell you whether or not to trust their FAQ, but I have heard this before too. As for power ratings, I would make sure that it tells how many channels can be driven at once at the specified power ratings. I have a kenwood vr-407 (much lower model than the 6060) but the specs are quoted in a very similar way. it doesn't give FTC standard ratings except in stereo power. the rest just says "effective power" or something like that. It doesn't say at all how many channels can be driven at the effective power, or how the effective power was measured.

 

[ThomasL]

I found this link while doing a quick usenet search:
http://www.hometheatermag.com/showarchives.cgi?85
It seems that THD ratings aren't that reliable or important.
cheers,
--tom

 

[Ken Shiring]

I think I can help a little with these questions.



RMS (Root Mean Square) power output is a way of measuring the power of a signal that is constantly changing. This means the RMS power value would be equivalent to the power of a device driving a purely constant (voltage)x(current) value of the same power.



That being said, the only thing that RMS power is useful for is to figure out how loud it can drive your speakers. If you do a search on this forum, I know that several members have posted handy watts-to-dB tables that you can add to your speaker sensitiviy to determine overall sound pressure in your room. The summary here is that more sensitive speakers require less power to be loud. Other than that, RMS power available has very little at all to do with sound quality.



I am highly suspicious of manufacturer's power specs. Invariably, they creatively report them to look as favorable as possible. If I were choosing a receiver (or amplifier), the two power characteristics I would look at are :

• Power available for a single channel into a 4 ohm load
• Power available for each channel, all channels driven, into 4 ohm loads[/list=1]
  
  
  
  Measurement of power is a complicated thing. There are many factors that affect how much power is available to you at any given point in time :
  • How much the power supply is capable of sourcing
  • How many output transistors drive each channel
  • Quality of the output stage transistors (current capacity)
  • The impedance of the load (8 ohm, 4, or even 2 or less)
  • How many channels the unit can drive
  • How many channels are being driven hard (loud sounds playing)
  • The size of the resevoir capacitors, and their ability to source large instantaneous currents for the amp stages
  
  To a non technical person, this is a hard thing to keep straight. I have found that the first two answers to your question above to be the best measurement of the power of an amplifier without getting into the specific issues I pose above. Question 1 is designed to figure out the limitations in the output stage of one amplifier (assuming all the channels have the same amp design). Question 2 is designed to figure out the limitations of the power supply of the amp. Invariably, the biggest limitation in a mass market receiver (or amp) is in the power supply. The power supply will always be the biggest bottleneck to delivering power.
  
  
  
  The best course of action for obtaining this information is to go to independent testing organizations. Most home theater magazines do a decent job of measuring these things (similar to a Consumer Reports for audio ). Personally, I believe that Sound & Vision does the best job of measuring these parameters, and presenting them in a legible fashion in their magazine. There are plenty of reviews online for any gear imagineable, so I would surely look there also.
  
  
  
  As far as DAC ratings go, you are asking a highly contentious question. Asking whether 192 kHz DACs sound better is like asking someone what to believe about cable quality . I urge you to do a search and try to take a sampling of some of the opinions from the members here. Personally, I have not had enough experience comparing DACs to give you an informed opinion. However, I will say that a 192kHz DAC is not automatically better than a 96kHz one.
  
  
  
  Good luck, and I hope this information can help you make a better decision .