• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Review and Measurements of Cambridge DacMagic Plus

daftcombo

Major Contributor
Patreon Donor
Joined
Feb 5, 2019
Messages
1,094
Likes
825
#21
Hi,

Can someone explain me the use of three filters ? (linear, minimum, steep)
Which one sound best ? and why do the two others exist ?

Cheers.
 

pma

Member
Joined
Feb 23, 2019
Messages
12
Likes
28
#22
About filters (from DM+ manual):

The Linear Phase filter is a filter offering low ripple in both the pass and stop bands, and what is known as constant group delay. Constant group delay means that audio signals of all frequencies are always delayed by the same amount when passing through the filter. All audio is therefore fully time-coherent at the output.
The trade-off with this type of filter is that due to internal feed-forward in the DSP, its impulse response will exhibit some pre-ringing. In other words, when excited with a theoretical impulse, the output has both a small amount of pre- and post-spike amplitude ringing (albeit well damped).

The Minimum Phase filter is a filter that offers even lower ripple in the pass and stop bands. Unlike the Linear Phase filter, group delay is not constant so some timecoherence is lost; however, phase shift is low and the particular benefit with this filter is that the
impulse response exhibits no pre-ringing.

Steep filter is a linear phase filter that has been optimised for stop band attenuation of close-in aliasing images. Here we have traded a little attenuation of the very highest frequency response (-2dB at 20kHz) and a little more pre- and post-ringing for a very steep attenuation just outside the pass band. The Steep filter is able to attenuate aliasing at 22kHz by some 80dB.
 

graz_lag

Major Contributor
Joined
Oct 13, 2018
Messages
1,045
Likes
893
Location
Le Mans, France
#23
Hi,

Can someone explain me the use of three filters ? (linear, minimum, steep)
Which one sound best ? and why do the two others exist ?

Cheers.
Just a bit out of topic ... The reasons why manufacturers bother with these digital filters is hard to understand to me ... since we are ideally looking for the most reasonable accurate output resembling to the input ...
For sure these filters add more appeal to a machine, as their audibility effects vary from "me" to "you" to the "next" ...
Ohh ... these filters also represent additional impedance within the circuit ...
 

somebodyelse

Active Member
Joined
Dec 5, 2018
Messages
193
Likes
137
#25
I agree with @VeriUpgrading the stock PSU into a nice linear one is always a good step from an engineering point of view, whether the results of that upgrade are audible that is a totally different subject ...
I'd argue going for the more expensive option while making no difference to the output is bad engineering.
 

graz_lag

Major Contributor
Joined
Oct 13, 2018
Messages
1,045
Likes
893
Location
Le Mans, France
#26
The reason why DAC chip manufacturers added minimum-phase filter options was initially to provide the shortest possible delay compared to linear-phase filters, for certain real-time applications.
Indeed.
My feeling is that today filters are used by DAC' designers to "cure" ills in the circuit.
Las but not least, I have concerns abt. these filter effects on the bit-perfect data stream of our much loved bits.
 

JJB70

Major Contributor
Patreon Donor
Joined
Aug 17, 2018
Messages
1,326
Likes
2,398
Location
Milton Keynes, England
#27
There is a major selling point of this unit for me. I'll admit that this is very parochial and may be completely irrelevant for most, but I can drive to my local Richer Sounds (5 minutes, just adjacent to Milton Keynes Central railway station) and buy one of these. The price is not that much more than Topping, SMSL etc alternatives but I have the assurance of a local shop which happens to have a very good record for customer service and after sales support. If anything goes wrong on gear I've bought from them I can drive to the shop and my experience of their handling of such things is very positive. That is worth a lot to me, I know the argument is that these things are cheap, but they're not that cheap (personally I don't consider £250 throw away money).

On the technical performance, despite being a decade old the measured performance remains perfectly respectable and kind of demonstrates that DACs have been technologically mature for a long time despite marketing claims trying to convince us that they've been racing along technologically and inferring that if you replace last years model with this years replacement it'll transform your life. The DAC in my CD player is something like 25 years old and remains a good, solid performer.
 

graz_lag

Major Contributor
Joined
Oct 13, 2018
Messages
1,045
Likes
893
Location
Le Mans, France
#29
I'd argue going for the more expensive option while making no difference to the output is bad engineering.
I agree over engineering is not a good approach ...
However, IMHO it is hard to accept that machines sold @ £350 as was the case for the DM+ back in 2012 come with £2.5 PSU ...
Because of some direct experiences, I have the tendency to pay some attention to the power section of my setups. ;)
 
Last edited:

graz_lag

Major Contributor
Joined
Oct 13, 2018
Messages
1,045
Likes
893
Location
Le Mans, France
#30
... The DAC in my CD player is something like 25 years old and remains a good, solid performer.
Indeed, particularly thanks to the '80s output "gentle" slope filters to reduce phase shift in the audible frequencies.
 

BYRTT

Active Member
Patreon Donor
Joined
Nov 2, 2018
Messages
160
Likes
181
Location
Denmark (Jutland)
#33
The reason why DAC chip manufacturers added minimum-phase filter options was initially to provide the shortest possible delay compared to linear-phase filters, for certain real-time applications.
Have you noticed same behavour as when one measure those IIR (minimum phase) filters they often can look a bad idea, or is that error in ones chain because often I/O clocks is not from same PCB or is there something about below.

Concern is when those filters is so steep a slope and being IIR they add a wide pass band phase domain distortion deep low into midrange area probably because they have to happen below nyquist limit which is not far apart filter target setting itself.

Examples is below where first (green) is a ES9023 USB DAC that will suppose is internal set as a FIR (linear phase) filter and second (blue) is a ES9018 USB DAC that will suppose is internal set as IIR filter, now look at grey phase traces which is asking REW how IIR phase should look for that amplitude response inside a 44kHz rate, DAC with FIR filter looks pretty close but DAC with IIR filter looks distort timing deep down and wide in passband and probably why some DACs can sound some weird or lets say stand out from any normal phase performance by the book.

1000c.png
.
 
Last edited:

spittiz

New Member
Joined
Feb 7, 2019
Messages
1
Likes
0
#34
I've used this as a DAC for like 7 years on my computer, feeding both a headphone amp (Lake People G109) and a speaker amp (NAD c326bee). Luckily you can disable the horrible volume control.
 

graz_lag

Major Contributor
Joined
Oct 13, 2018
Messages
1,045
Likes
893
Location
Le Mans, France
#36
Nice, now if only someone could lend his Audiolab M dac..
Yes, another machine that has got a lot of fans out there and that keeps a very good value in the second hand market. (Despite the newer + version.)
 
Joined
Nov 23, 2018
Messages
32
Likes
30
#40
@amirm How about the headphone out performance? Is it worth talking about?
on my mr speakers aeon flow open , the volume needs to be like 90% on the cambridge and clips slightly on very bass heavy songs, on the other hand when i upgraded to the jds lab atom feeded by the dac magic , it sounds much better (especially noise floor is noticeable and less bass bloom more impact) , volume knob is at 12 oclock on the atom. It would be great if @amirm could post some data regarding the headphone out
 
Top Bottom