The Absolute Sound disects SAM

[Pim]

Interesting read.

http://www.theabsolutesound.com/articles...amplifier/

[David A]

Definitely an interesting read but it doesn't answer the big question I still have: just what is that amount setting doing? What does it change? I can only assume it functions a bit like a bass tone control, boosting the level of the frequencies affected by SAM as you increase the amount.

It would really be nice if we could get a decent explanation of just what the processing applied by SAM actually is.

[daniel.avasilichioaei]

The explanation about SAM (including SAM %) is here: https://www.youtube.com/watch?v=AcLYb4sBhwQ.
SAM % is affecting bass extension level, while phase correction and drive protection are not affected by SAM % adjustment.

[ogs]

Very nice read! There is much technology to admire in Devialet designs! Thanks for posting the link @Pim .

[Pim]

It's a lot more noticeable on stand mounts David. The bass goes deeper(Lower in frequency) but not louder.

[David A]

I'm sorry but that does not tell me what I'm interested in learning. It shows how a profile is made but what I'm interested in is seeing how the processing which is applied changes as you change the % setting on one hand, ie what adjusting the % does to the signal sent to the speaker while your volume setting remains constant, and on the other hand what happens to the signal as you change volume level while the % setting is kept constant.

What we get in that video, and everything else I've seen from Devialet on SAM, is some sweeping generalisations with no detailed description of what happens to the signal sent to the speaker when the SAM % setting and/or the volume setting are changed. I know how things sound when I make those changes with my speakers but I would like to see how the signal changes, whether the changes with % setting and with the volume setting are strictly linear or whether there is a particular tailored adjustment made which varies from speaker to speaker, and I'd like a more detailed explanation of what is going on when the % setting is set to 0%. In other words, I'd like to have a more detailed understanding of what's going on than I can get from fairly generalised explanations like the one in that video.

This isn't because I think SAM doesn't work or anything like that, I think it works and I am using it at the moment but I have real difficulties with the % setting. Currently I have it set to 0% because I find that even setting to as low as 10 to 15% with my speakers in my room results in tonal changes which cause a hardening to the bottom of the female vocal range and below which I don't like. I'd like to know why I hear that even with a very low % setting but I have no problems with that kind of tonal shift when I set the % to 0%.

My experience is that understanding what's going on with something can often help you to use it more effectively and get better results. I'd like to understand what's causing that tonal shift I hear and the only thing i can think of which would do it is that the % setting is applying a boost to the signal level over a range of frequencies and I'd like to be able to understand what the "shape" of that boost is and how it varies as I change the % setting and as I change my volume setting.

[David A]

It's a lot more noticeable on stand mounts David. The bass goes deeper(Lower in frequency) but not louder.

I used it with a stand mount, the Dynaudio Contour 1.3 SEs I was using before I swapped to Focal Sopra 2s, and I've used it with the Sopras. I actually find the change that concerns me, the hardening of tonal character I mentioned above, is more noticeable with the Sopras, I can't recall noticing it with the Contours. I also think it became more noticeable after the CI board upgrade to my then 130 so I wonder if there was something in the change in the OS when we got the CI board which had an effect on SAM in some way, did they change something which interacts with SAM in some way?

I think there is an increase in loudness as the % setting increases but I also think that there may well be a reinforcement of our perception of lower frequencies when their phase angle is more closely matched to the phase angle of their overtones and it's possible that what I'm hearing is partly a result of low fundamentals being more in phase with their higher frequency overtones.

[ogs]

It's a lot more noticeable on stand mounts David. The bass goes deeper(Lower in frequency) but not louder.

I used it with a stand mount, the Dynaudio Contour 1.3 SEs I was using before I swapped to Focal Sopra 2s, and I've used it with the Sopras. I actually find the change that concerns me, the hardening of tonal character I mentioned above, is more noticeable with the Sopras, I can't recall noticing it with the Contours. I also think it became more noticeable after the CI board upgrade to my then 130 so I wonder if there was something in the change in the OS when we got the CI board which had an effect on SAM in some way, did they change something which interacts with SAM in some way?

I think there is an increase in loudness as the % setting increases but I also think that there may well be a reinforcement of our perception of lower frequencies when their phase angle is more closely matched to the phase angle of their overtones and it's possible that what I'm hearing is partly a result of low fundamentals being more in phase with their higher frequency overtones.

I have not thought very deep about this, but I believe SAM is a "closed system" in the sense that the DSP gets detailed info on voltage, current and frequency going to the speaker continuously. This is compared to the SAM profile for the speaker and the DSP makes adjustments accordingly. So SAM depends on a lot of information from the amp stages it is part of - and would not work standalone on an 'unknown' amplifier. ADH does something similar. In the drawing below the CTRL signal is embedded in the feed from the Class-A stage to 'cancel out' unwanted things in the Class-D stage. The CTRL signal is changing with level. Same with DPM. Power demand is calculated continuously based on the music signal and volume level and the power supply delivers based on this.

   

[daniel.avasilichioaei]

This isn't because I think SAM doesn't work or anything like that, I think it works and I am using it at the moment but I have real difficulties with the % setting. Currently I have it set to 0% because I find that even setting to as low as 10 to 15% with my speakers in my room results in tonal changes which cause a hardening to the bottom of the female vocal range and below which I don't like. I'd like to know why I hear that even with a very low % setting but I have no problems with that kind of tonal shift when I set the % to 0%.

My experience is that understanding what's going on with something can often help you to use it more effectively and get better results. I'd like to understand what's causing that tonal shift I hear and the only thing i can think of which would do it is that the % setting is applying a boost to the signal level over a range of frequencies and I'd like to be able to understand what the "shape" of that boost is and  how it varies as I change the % setting and as I change my volume setting.

Your issue may be relating to this bug for current firmware + SAM + tone adjustment: https://devialetchat.com/Thread-Bug-for-...-DOS-2-2-4.

Did you ask your questions to Devialet team?

[David A]

Your issue may be relating to this bug for current firmware + SAM + tone adjustment: https://devialetchat.com/Thread-Bug-for-...-DOS-2-2-4.

Did you ask your questions to Devialet team?

I don't think the bug you mentioned is my problem. What I'm hearing depends on the SAM % setting and occurs with Bass set to zero (I  always run with Bass and Treble set to zero). It becomes more noticeable as the SAM setting is increased.

I haven't tried asking Devialet, basically because I tend to run with SAM either set to 0% or extremely low, less than 10%, when I don't notice it, or I use a configuration file with no SAM parameters. I don't feel a need for increased bass extension with the Sopra 2's in my room with the music I listen to but the correction applied at the 0% setting does produce a difference I like.

I don't feel a desire to have Devialet really change anything because I can get a result I like with things as they are. I'd hate them to find a bug on the basis of a report from me, fix it, and then find that I don't like the result after the fix. As I said, I'd like to have a better understanding of what's going on, what is changing in the SAM DSP processing as you change the SAM setting and also as you change volume.

I just re-read the comments on SAM in Jim Austin's review of the 140 Pro in December's Stereophile. He reports measuring an increase in SPL at some—not all—pure tone test signals with SAM turned on and he asked Devialet about that. Their response was that it had to do with room interactions which he said he didn't understand but that dialling SAM back to below 40% solved the problem. That sounds like he could have been noticing a similar issue to the one I notice. I think I can understand how it could be a room interaction. If the SAM % setting dials in an increasing amount of bass boost over the range covered by SAM, the increased level at some frequencies could be exciting a room mode and if that is the case, reducing the setting could well reduce the noticeability of the issue. If that's the case then there's nothing for Devialet to "fix" in my case, I just have a room mode at a frequency in the lower range of female voices that is being excited to a level I notice once I increase my SAM setting to somewhere around 10-15%. Anyone else who doesn't have a room mode at that frequency isn't going to notice what I'm hearing and there's no bug to fix, it's likely to be a standing mode issue in my room. The problem that I have is that Devialet just seem to like to not give people the information they would like to have  and, given that they weren't all that forthcoming with information when asked a very specific question by Stereophile's editor who was reviewing one of their amps, I really can't see them giving any more information to "mere owners" like you or I. People have been asking them questions about SAM for a few years now and we still really don't know much more than what they initially told people when they introduced it. They simply don't like providing information.