Thursday, September 8, 2016

Famciom vs. AV Famicom External - Internal Audio Mixing

There is a myth that the AV Famicom is too quiet when it mixes internal audio with external audio.  The myth goes that the external cartridge audio drowns out the internal audio from the console and gives an unbalanced and unfair impression of what the programmer intended the music and sound effects to sound like.  The conclusion is that an original Famicom, preferably an earlier model, is the ideal way to experience Famicom audio.  However, this conclusion is too simplistic and the internal/external mix is not as extreme on standard Nintendo Famicoms and AV Famicoms as one may be led to believe.

Of course Famicom audio has its own problems.  The first problem is that genuine Famicom audio is encoded into RF and decoded in a TV.  The baseline audio has a buzz and the output of the audio sounds like it was run through an oppressive low-pass filter.  The second problem is that playing a Famicom with its RF video and hardwired controllers is something of a chore.

I have made some recordings of several games which use Famicom expansion audio and internal Famicom audio.  The games in question are :

Zelda no Densetsu (Famicom Disk System, The Legend of Zelda)
Akumajou Densetsu (Konami VRC6, Castlevania III: Dracula's Curse)

Zelda no Densetsu was being run off a real FDS RAM Adapter and Akumajou Densetsu was run off a real cart.

The AV Famicom is a HVCN-CPU-02 with laser marked 2A03H and 2C02H CPU and PPU.  This is a very late AV Famicom.  Nintendo stopped manufacturing AV Famicoms in 2003.

The Famicom is a HVC-CPU-07 with 2A03E and 2C02E CPU and PPU.  This is a probably the most common Famicom PCB revision.  It has the AV board connected via a ribbon cable, not soldered to the main PCB via the RF shield.  Nintendo made this model with revision E and G CPU and PPU chips from 1984 until 1988.  In 1988 it switched to the HVC-GPM-0x motherboards, which have the RF shield soldered to both PCBs.  These Famicoms tend to have audio like the AV Famicom.

Most of the Famicom Disk System games were released from 1986-1989, so they would tend have been programmed for the older Famicoms.  Akumajou Densetsu and Rolling Thunder were released in 1989, so they too may have used the older Famicoms for development and testing.  Other games like Lagrange Point (1991) and Gimmick (1992) were released well into the newer Famicom production, so they may have been intended for later systems.

Both consoles are unmodded as far as sound goes.

The AV Famicom is being recorded through a Nintendo-manufactured Stereo AV cable.

The Famicom, set to Japan Channel 2, U.S. Channel 96, is being routed to a VCR via a well-shielded coaxial cable.  The VCR then separates the RF into composite video and separate audio.  The audio output through the RCA jack is being recorded.

The Famicom/NES internal audio has five channels mixed into a single monaural output, rectangle, rectangle, triangle, noise & PCM.  The VRC6 has three audio channels, also mixed into a single monaural output, rectangle, rectangle, sawtooth.  The FDS has one wavetable audio channel.

In some clips, the expansion sound is used only for music.  In other clips, it is used only for sound effects.  In Zelda, the FDS channel is combined with the internal audio for the opening music, but most of the game uses just the internal audio for music.  The FDS channel handles many of the sound effects.  In Akumajou Densetsu, the three VRC6 channels are used solely for music

In order to try and narrow down the cause of the difference between the two Famicoms, I decided to record the internal volume only.  You can tap the internal audio from the Famicom Expansion Port.  I decided to use this method to eliminate any amplification differences between the RF module on the Famicom, which the AV Famicom does not have.  The audio paths between the two devices should be identical at the point where the audio is routed to the port.  I recorded pure tones with the 240p Test Suite.  The tones start at 8KHz and then divide by 2 until you get to 32Hz.  All the tones are produced using the triangle wave, which is the closest the NES can come to a sine wave.  The final tone is a 1KHz square wave.

You will note the increased loudness of the volume of the internal audio on the Famicom as opposed to the AV Famicom.  It has been shown that the changes to the audio amplifier in the GPM and AV Famicoms made the internal audio volume lower compared to the expansion audio volume.


  1. Dude you have been on a roll lately and I've been loving it. These audio comparisons are really good. I keep referring back to your post on one of the forums regarding restoring the 2nd controller mic for the AV famicom by adding a chip from the original famicom. It seemed like you were just hypothesizing but did you ever attempt that? Really interesting to have the ultimate 8 bit setup that can handle any game or controller from either side of the pond.

  2. My refined idea is here :

    If I ever decide to do it and it works, I will post it on the blog.

  3. This is a very interesting find, thanks for preparing all those clips. I've been looking into a solution to remedy this issue as I have just ordered a Famicom AV from Japan.. So far I have found that some people have used resistors to tone down the external audio, but this also degrades some of the quality as a whole degrading favourable percussion sounds for example. I wonder if somehow the internal could just be amplified instead, simply with an adjustable switch before streaming back to the AV output. I'm not an expert on how these things work but would something like this be possible?

  4. Actually, the original Famicom is clipping in the triangle wave comparison, but the AV Famicom is not.

    Here's an image of the zoomed in wave forms.