PCM Has No Bass

Spottedfeather · Sep 25, 2024

I was having trouble hearing a certain scene of dialogue. I was told to change bitstream to PCM. When I did, the dialogue WAS easier to hear. The problem is that if I use PCM, there is practically no bass.

For example, during the intro of Jurassic Park, when the titles appear, there is a huge deep boom noise. With bitstream, you can almost feel the boom in your chest. But if I run that scene with PCM, there's no bass at all. Going from bitstream to PCM is the only setting change I made...other than turning off BD secondary audio.

Any ideas why this is happening ? Should I turn the subwoofer up ? Currently it's set at +2 on mode settings, while it's set at, I think, 0 on the setup done with the microphone. I could be wrong about these settings, though

lovinthehd · Sep 25, 2024

Need more info about your source, gear and settings involved but at a guess your PCM is 2.0 channel, rather than multich PCM (LPCM), and has no LFE.

Sawtaytoes · 2024-10-04T00:55:20-0500

Interesting. I'm noticing a similar issue.

First, I think you should be using bitstream audio (which supports PCM too) rather than PCM audio output.

My Similar Issue

I have 2-channel PCM files on shows I've imported from Japan. I rip the discs and add subtitles, but I've found there's no bass in the playback like there is on my PC.

Switching to the AC3 track, it's like the sound opened up. Instead of sounding like a 64kbps MP3 with no bass, it sounded like a regular-quality audio track with tons of bass and sound that had much more atmosphere when upmixed.

The only thing weird about the PCM track is it's 24-bit 48kHz. I'm using Plex, and this page says that's not supported even if the Shield itself supports this audio format:

I'm thinking your player might have the same issue. It might be converting 24-bit Dolby TrueHD or DTS-HD MA to 16-bit PCM. Whatever it's doing, it's removing the bass. If you listen closely, it might also be making the audio sound very low-bitrate-MP3 compressed.

My Gear

I have HDMI passthrough enabled on both the Shield and in Plex.
I disabled the PCM to Dolby Digital conversion that the Shield has on by default.
My receiver is the Marantz AV 10 and my TV is the LG G2 OLED.
My connections are Shield → Receiver → TV.
I have the Dolby Surround upmixer enabled; not Direct, but it's the same regardless of what setting I try.
I made an AVSForum post with more details (including screenshots) here: PCM audio with no bass on NVIDIA Shield & Plex? | AVS Forum

I thought it might be a Plex issue, and it might be, but I'm also wondering if it's an AVR issue where the Marantz AV 10 simply doesn't support bass output with PCM audio.

Trebdp83 · 2024-10-04T10:17:54-0500

Without a multichannel track containing LFE, an AVP/AVR will send the lower frequencies of the two channels to the subwoofer based on the crossover setting of the Small Front Speakers.

If the Front Speakers are set to Large, no lower frequencies will be sent to the subwoofer unless LFE+Main is selected in the subwoofer setting concerning Denon/Marantz models.

As always, information concerning all of the devices and settings in a system are not only helpful, but essential in trying to figure things out.

dlaloum · 2024-10-05T21:05:54-0500

in PCM mode you are sending the discreet channels...

Your AVR then determines how to process cross over and mix those channels.

The LFE (x.1, low frequency effects) channel, is often mistaken for the bass... as many setups have the Sub output labelled LFE...

The issue then is how does your AVR manage the main channel and LFE bass?

If you have your mains "crossed over" (and not set to full range) - then, in theory, the bass from the mains, below the XO frequency, should be sent to the Sub, along with the LFE channel - so the LFE and the Bass from the Mains would be mixed together on the sub output.

Many setups nowadays are based on mains that have no reall bass output, due to everyone having a sub, and smaller "satellite" speakers are easier to place, live with, and get WAF ...

The trouble is, if you then try to run the in "pure" modes (ie: each channel is sent exclusively to its speaker, and no crossovers or mixing is invoked) - you will find the sound lacking in bass.

Typically when you switch from one mode eg: bitstream to another eg: pcm - the AVR is configured to select a specific processing method for each mode by default (on some this is configurable, on others not so much!) - that default mode may be a "Pure Direct" style mode (no XO's) or it might be a blended/mixed mode (use the sub for bass from all channels) - but without further investigation, forum members like myself out in the virtual space, cannot tell.

This is what I would be investigating, were I in your shoes.... what mode is the AVR in when running bitstream, and what mode when running PCM... there is a very high likelihood that the audible difference is in that mode.