13 January 2021, 14:12 | #61 | |
Registered User
Join Date: Oct 2009
Location: Germany
Posts: 3,303
|
Quote:
|
|
13 January 2021, 19:28 | #62 | |
Computer Nerd
Join Date: Sep 2007
Location: Rotterdam/Netherlands
Age: 47
Posts: 3,751
|
Quote:
Yes, i was wrong about the audio being 14 bit Thomas Richter is certainly right about measuring. In this case measuring using the ear is enough to determine that the audio is indeed not 14 bit, or even 11 bit as it so turns out. I wonder if Paula can't do better using the amplitude modulation feature. |
|
13 January 2021, 20:07 | #63 | ||
Registered User
Join Date: Jan 2017
Location: London, UK
Posts: 433
|
Quote:
Quote:
|
||
13 January 2021, 22:03 | #64 |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Paula's capabilities wrt. actually achievable bit depth in the 14 Bit mode are in the ballpark of 10-11 bit with ECS Paula, depending on the Amiga model. Two major factors contribute to the observed limitations:
a) DAC output levels are not linear with respect to the intended 8 bit source amplitudes b) the low volume channel is not synchronized in time and actual frequency to the high volume channel due to Paula's implicit resampling at volumes <64 What I disagree with are the estimated noise figures that started this thread. An SNR of 30dB corresponds an effective resolution of less than 5 bits. My own measurements return different results, consistent with theoretical expectations and existing publications. My baseline measurement in classic 8 Bit resolution landed at 45.8 dB (theoretical optimum: 49.9 dB, old papers around 42 dB). I observed up to 59.6 dB in calibrated 14 Bit mode (A4000) which amounts to a sad hard number of 10 Bit resolution. With some leniency towards correlated components of the noise figure (i.e. jitter in the low channel), generous rounding and a comparison of the noise floor with 11 bit ideal quantizers, one might be inclined to call it close to 11 bit. I've updated my Paula writeup with Details to these measurements. The PDF can be found here |
13 January 2021, 23:15 | #65 | |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Quote:
I did some preliminary of testing vol 63+vol 1 channel stacking back in the 90s and abandoned that quickly due to artifacts of the implicit resampling. Last edited by buggs; 13 January 2021 at 23:16. Reason: formatting |
|
13 January 2021, 23:48 | #66 | |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Quote:
True, any frequency well below the 3dB cutoff is unimpeded. The pre-emphasis has to compensate for 15 dB attenuation around 18 kHz (A500/2000/4000), 12 dB for A3000 and 4 dB for A1200. The latter is hardly of consequence, ofc. But this process involves a trade-off between the dynamic range of the output signal and filter headroom. A near flat frequency response out of an Amiga is nice but won't help wrt. SNR. That's why I left it out of my experiments. Concerning the calibration update: I don't expect a large impact on measurements with sine tones at 0 dBFS. I've only noticed (and disliked) the quantization table issue with signals of low amplitudes. |
|
14 January 2021, 00:43 | #67 | ||
Registered User
Join Date: Jan 2017
Location: London, UK
Posts: 433
|
Quote:
Quote:
|
||
14 January 2021, 12:15 | #68 | |
Registered User
Join Date: Dec 2014
Location: germany
Posts: 439
|
Quote:
Do you have an estimate what fraction of the total noise is due to that internal resampling? What SNR would be achievable at 55.4 kHz? It's rather pointless for practical purposes because it'S such an uncommon sampling frequency, and good quality resampling probably beyond the capabilities of an Amiga CPU. |
|
14 January 2021, 13:04 | #69 | |
Registered User
Join Date: Jul 2015
Location: The Netherlands
Posts: 3,409
|
Quote:
All this does make me wonder about two things (one was kind of answered, but I didn't really get the answer so maybe someone can clarify?):
|
|
14 January 2021, 13:39 | #70 | |
Registered User
Join Date: Dec 2014
Location: germany
Posts: 439
|
Quote:
I am however not 100% sure I understand everything correctly, and I had more of a glimpse at the paper than really working through the math. Last edited by chb; 14 January 2021 at 13:49. |
|
14 January 2021, 15:12 | #71 | |||
Registered User
Join Date: May 2001
Location: ?
Posts: 19,645
|
Quote:
And to add insult to injury, most these people don't have even half the Amiga knowledge Thomas does. Quote:
Quote:
It doesn't matter how good you THINK you hear (excuse us, "god ear"), you're not a measuring device and what's being discussed and posited here, is hard, solid, concise data. You're the kind of people that say "vinyl sounds better". |
|||
14 January 2021, 15:25 | #72 |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
Coincidentally I wrote:
"and about vinyl, yes for me also sound 'better' than CD, it is more colorful and full-bodied (and I'm not talking about the 'physical' or 'measurable' qualities of sound at all)" Otherwise there would be no reason for someone's preference in something and even this entire forum would not make sense at all. |
14 January 2021, 16:41 | #73 | ||
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Quote:
In case of digital resampling, especially the approximation of point sampling (or nearest neighbor), is the more important other side of the coin. Nearest neighbor resampling can be decomposed into two fundamental operations: convolution of the input signal with a rectangle (=implicit interpolation), followed by sampling at the new rate. The frequency domain correspondence to the rectangle is part of the new spectrum and introduces the relevant noise. Quote:
55 kHz: I could not get any of my Amigas to play sound at 55.4 kHz properly. The maximum I could obtain was 54.5 kHz and I didn't do any measurements at that rate. Last edited by buggs; 14 January 2021 at 16:41. Reason: I never get the newlines right here. |
||
14 January 2021, 16:47 | #74 | |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Quote:
|
|
14 January 2021, 16:58 | #75 |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
|
14 January 2021, 17:02 | #76 | |
Registered User
Join Date: May 2016
Location: Rostock/Germany
Posts: 132
|
Quote:
As luck would have it, I was just handed an A600 for fixing. And unsurprisingly by now, that A600 has the same filter as A500/2000, 100nF+390Ohms. |
|
14 January 2021, 17:17 | #77 |
Computer Nerd
Join Date: Sep 2007
Location: Rotterdam/Netherlands
Age: 47
Posts: 3,751
|
I performed my own test by ear after Thomas Richter posted his test results and I came to the same conclusion. Don't be so quick to dismiss the ear. In this case it becomes crystal cleear very quickly if the ear is good enough, and it certainly turned out to be the case. Might be a coincidence, of course
|
14 January 2021, 17:30 | #78 |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
Problem here is that Paula is a strange beast, it's not like the usual PCM or PDM emitter of today. It' a mixed PCM/PWM state machine, prone to distortions due to her inner working. Add to this: specific period granularity, different phase for the channels, different filters, different components, different D/A separations, home made 'software' linear calibration (that any technician would shiver to conceive such 'unreliable' thing )... Many of these properties are not bad per se (far from it!) but they make it difficult to compare it with the existing.
Yes, you can measure the 'math quality' of the sound and decide that Paula is 10, 11, 12 bit or alike (I am not among those who think it is even remotely similar to 14 or 16bit). But the 'reconstruction' that Paula do from the discrete quantized bits is pretty unique and not so simply comparable with the existing. What are the conditions that allow it to perform at its best in the 'emulation' of the original signal? I don't think there is anyone here with a precise answer.. So blind test is probably a path to try (as mentioned in a previous message) . But under the conditions of the first post Thomas is right. |
14 January 2021, 17:38 | #79 | |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
Quote:
http://eab.abime.net/showpost.php?p=...6&postcount=92 |
|
14 January 2021, 17:50 | #80 |
Registered User
Join Date: Jul 2015
Location: The Netherlands
Posts: 3,409
|
Well, the reason for asking is kind of like this: suppose you have a sample playing at a non-maximum volume and then use Paula's amplitude modulation on it. What happens?
Does the amplitude modulation simply "overwrite" the volume setting of the channel with a new one, or does it affect the output separately? If it does the latter, you might be able to reach volume levels that are not normally possible, which might be interesting. Or does it perhaps merely alter the digital value of the sample pair currently read? I guess I'm asking if it's:
Last edited by roondar; 14 January 2021 at 17:54. Reason: Order of text in my post was confusing. |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
Thread Tools | |
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
"Voices8" 8 Channel Soundtracker "DemoSongI" song - "This is the Amiga with 8 Voices" | DemosongIHunter | request.Music | 45 | 23 May 2022 20:07 |
IDE 40/44 pin adapter to work in Amiga 1200,a bit "dirty" hack. Possible? | hda | support.Hardware | 4 | 11 September 2020 00:05 |
Question on audio settings: Should I use UAE "sinc" or OpenAL "4-point sync" or both? | Dr.Venom | support.FS-UAE | 3 | 14 September 2017 08:22 |
Amiga Power "Games Massive" Audio Tracks | twcustom | project.TOSEC (amiga only) | 4 | 21 July 2016 21:09 |
"Bit för bit" demo (Swedish TV-show, hard to find!) | Ziaxx | request.Demos | 5 | 10 March 2009 18:38 |
|
|