Archive for the ‘Miscellaneous’ Category

Home Theatre Receiver Subwoofer Offset

Sunday, May 30th, 2021

When testing receiver audio latency, I noticed that some receivers were able to extract low frequencies of an analog stereo source to send to a subwoofer with zero delay to the left and right speakers. This took me by surprise, because I expected the low frequencies for the subwoofer to be digitally extracted from the analog source signal, which would take some amount of time. This lead me to suspect that there might be an offset on the subwoofer’s output compared to the output of the left and right speakers when extracting low frequencies to create a 2.1 output from a 2.0 input.

I tested a few receivers for an offset on the subwoofer’s output and the results were interesting. All receivers seem to have some amount of an offset to the subwoofer, even when operating in Direct 5.1 mode where there is a dedicated subwoofer channel in the audio stream. This offset, as I suspected, was almost always larger when the receiver needed to extract low frequency sounds, i.e. from a stereo input.

Left and LFE channel output from a Denon AVR-S650H that is given a 5.1 input with the exact same audio stream sent to all channels
Left and LFE (subwoofer) channel output from a Denon AVR-S650H that is given a 5.1 HDMI input with the exact same audio stream sent to all channels

I expected that the Audyysey speaker calibration on my Marantz receiver would be able to detect this offset and correct it by calibrating my subwoofer position to be a further distance, thus adding a delay to other speakers. Unfortunately, it seemed to only detect a 0.6 foot difference, which may have been partially due to my physical speaker placement, and did not negate the offset entirely. Strangely, only when operating in small speaker stereo mode, my subwoofer offset measurements for this receiver are much higher than other modes, but also much lower than expected with the distance setting applied. Put simply, further testing is needed to understand this subwoofer offset behaviour and how it is resolved by speaker calibration.

Speaker distances calculated by Audyysey.
Speaker distances calculated by Audyysey. During calibration, my Front R and Subwoofer were placed directly beside each other, approximately equidistant to the calibration microphone.

Here’s a full list of my measurements for a few different receivers in CSV format and in a Goolge Sheet.

While I was reviewing these measurements, I took note of some other behaviours that the receivers had. One of the receivers, the Pioneer VSX-933, defaulted to an inverted phase on its subwoofer output, but only for some input types/sound modes.

Pioneer VSX-933 sometimes inverts subwoofer phase
Pioneer VSX-933 sometimes inverts subwoofer phase

Also, all but the older Sony STR-DH540 filtered its subwoofer output with a low pass filter when it was configured to have large speakers and a dedicated subwoofer channel on the HDMI input.

Almost all receivers filter their subwoofer output
Almost all receivers filter their subwoofer output

For some receivers, especially the Marantz NR1711, the subwoofer output was very noisy with high frequencies when extracting a LFE channel from a stereo input.

Marantz NR1711 subwoofer output is very noisy
Marantz NR1711 subwoofer output is very noisy

One last behaviour I found quite interesting was a modification of the low frequency sound in the left and right channels when extracting a LFE channel from a stereo input. It seems as if the low frequency sound wave is compressed at the beginning of output. This type of behaviour existed in all receivers that I tested, but it was least notable in the older Sony STR-DH540.

All receivers would compress the low frequency output of their main channel when separating a subwoofer LFE channel
All receivers would compress the low frequency output of their main channel when separating a subwoofer LFE channel

There are many challenges of making a good DAC, especially one that can separate out an LFE channel from stereo with minimal delay. I don’t know why these behaviours are common and I also don’t know if they may effect sound quality and crossover behaviour in a real-world situation. Regardless, it seems that even a simple “Pure Direct” mode on a receiver with a dedicated LFE channel on your input signal may result in slight offset between main and LFE channels.

More Quirks of the PreSonus Studio 26c

Monday, May 17th, 2021

A little over a year ago, I posted about some unexpected behaviour with the different output channels of the PreSonus Studio 26c. During my work of testing different audio DACs and receivers for audio latency, I noticed that the internal clock on this USB audio interface to be notably off compared to other audio devices I had. To verify this, I generated a simple test signal that had tick sounds at the 1 and 11 second mark with a constant tone played throughout. I played this test signal in WASAPI exclusive mode when on a Windows computer or using the default/built-in audio player on other devices and recorded the results using my onboard audio and the PreSonus Studio 26c. I then subtracted the number of recorded samples from 480,000 which was the expected number of samples for these recordings.

Output DeviceRecording Length: ASRock Z170 Extreme7+ Onboard (Samples)Error (Samples)Recording Length: Presonus Studio 26c (Samples)Error (Samples)
ASRock Z170 Extreme7+ Onboard480,0000479,91981
Presonus Studio 26c480,081-81480,0000
2013 Macbook Pro479,98614479,90694
Samsung Galaxy S8479,9946479,91387
iPhone SE Gen 1479,98812479,90892
Marantz NR1711 USB Playback479,9991479,91882
MSI GF75 THIN Laptop479,98020479,899101
Sony STR-DH540 USB Playback479,9982479,91783
Number of samples recorded for a 10 second 48 kHz signal.
Expected samples: 480,000

It seems quite clear that the Studio 26c internal clock is quite an outlier compared to any device I could find to test with. Thankfully this did not affect my results at all during my audio latency testing because the difference in clock was too small to affect a <100ms recording. But this type of offset could become substantial after only a few minutes of recording or playback!

These results seem to show that my ASRock onboard audio clock and the clock used in my Marantz and Sony receivers are effectively the same. If these three were assumed to be a “source of truth”, this would mean that the PreSonus Studio 26c clock is actually running at 47.92 kHz when it says it is running at 48.00 kHz. As expected, this inconsistency appeared in other sample rates as well. Simply stretching the audio by 1.00016875x will correct the recording to be closer to the intended sample rate.

In the control panel for the PreSonus, there is an option to choose which clock source the device uses, but unfortunately the only option that was available to me was to use the Studio 26c internal clock. I presume that higher-end PreSonus devices allow use of a different clock through this setting to make recordings and playback consistent between devices.

If I say a game is too short, what do I actually mean to say?

Wednesday, August 18th, 2010

The following text is actually a comment that I posted in response to a post by Ron Carmel of 2DBoy.

In response to “If I say a game is too short, what do I actually mean to say?”:

I think that many players and critics may base their definition partially off of the classic childhood meaning of “too short” which means that the game did not fulfill its purpose as a time-wasting mechanism… From personal experience, as a kid I played games to waste time and be mildly entertained at the same time (entertainment quality was less important back then). Being a kid, I became bored quite a bit and video games were my simple solution to this problem. Pokémon Blue was a good game because it wasted 143 hours of my life. It fulfilled its purpose… at the time.

To assume that all players expect video games to fulfil the purpose of “wasting time” is ridiculous, as most adults (I would guess) would not be looking for this element as strongly as when they had “all the time in the world”.

To go back to the original question, here is what I personally would be saying if I was taking this lazy shortcut:

“Because of the price that I paid for this game, I was expecting to receive more raw time in fresh, new experiences.”

Interestingly, this statement has a natural contrast which is: “This game was too repetitive”. In this contrasting statement, the meaning is actually /exactly/ the same (“Because of the price that I paid for this game, I was expecting to receive more raw time in fresh, new experiences.”) — but in this case, the game is “too long”. Or, said differently, it stretches the game experience too thin so that it does not maintain a “fresh”, “new”, or “novel” experience throughout.

I agree with William’s comment that it is definitely something that is an audience problem more so than a critic problem: But, that said, critics should also be careful of using these lazy shortcuts because they may not totally understand their audience and therefore may be failing in communicating effectively with them.

Sadly, today, “too short” inevitably spawns directly from price in the video game world. If all games were free, we would never hear of a game that was too short unless we were simply saying that we wanted more of it. In terms of marketing and finding the right price for a game, I think it is not possible at this time to have the general audience of the world (and therefore the critics) to change their mind about what they feel is the right amount of “fresh experiences” for the price that they pay. It’s something you have to feel out, understand, and get lucky with as a developer.

I’m not sure how this series of posts came to be organized, but I thought I’d record my thoughts as a developer – Other posts that were part of an industry-wide commentary by indie developers on the subject of short games are as follows:

Ron Carmel of 2DBoy

Jonathan Blow of Number None

Chris DeLeon

Dave Gilbert of Wadjet Eye Games

Matt Gilgenbach of 24 Caret Games

Michael Todd
Eitan Glinert of Fire Hose Games

Cliff Harris of Positech Games

Chris Hecker of Spy Party

Scott Macmillan of Macguffin Games

Noel Llopis

Peter Jones of Retro Affect

Lau Korsgaard

Martin Pichlmair of Broken Rules

Greg Wohlwend of Intution Games

Jeffrey Rosen of Wolfire

Steve Swink


Thursday, April 29th, 2010

Hello everyone,

Welcome to the beginning of series of articles that will be written as I experiment in the field of 3D computer graphics, math, and video game design. Throughout these articles, I hope to touch on integration of design patterns and maintainable software design practices and their application in rapid game prototyping and development.

Stay tuned, this should get fun! 🙂